Amanda Philp - Academia.edu (original) (raw)

Papers by Amanda Philp

Research paper thumbnail of Indigenous Health: ACTION on Prevention - 50th annual Australian Society for Medical Research National Scientific Conference

Rural and Remote Health, Jul 1, 2012

The 50th annual National Scientific Conference of the Australian Society for Medical Research was... more The 50th annual National Scientific Conference of the Australian Society for Medical Research was held in Cairns, Queensland, 13-16 November 2011. The theme, 'Indigenous Health: ACTION on Prevention' highlighted the direct action being undertaken by health and medical researchers, as well as allied health professionals, to improve long-term health outcomes for Indigenous Australians.

Research paper thumbnail of Insight into the selectivity of arsenic trioxide for acute promyelocytic leukemia cells by characterizing Saccharomyces cerevisiae deletion strains that are sensitive or resistant to the metalloid

The International Journal of Biochemistry Cell Biology, Feb 1, 2008

The genome-wide set of Saccharomyces cerevisiae deletion strains provides the opportunity to anal... more The genome-wide set of Saccharomyces cerevisiae deletion strains provides the opportunity to analyze how other organisms may respond to toxic agents. Since arsenic trioxide selectively kills human acute promyelocytic leukemia (APL) cells by a poorly understood mechanism we screened the yeast deletion strains for sensitivity or resistance. In addition to confirming mutants previously identified as sensitive to sodium arsenite, a large number of additional genes, and cellular processes, were required for arsenic trioxide tolerance. Of the 4546 mutants, 7.6% were more sensitive to arsenic trioxide than the wild type, while 1.5% was more resistant. IC 50 values for all sensitive and resistant mutants were determined. Prominent as sensitive was that missing the MAP kinase, Hog1. The most resistant lacked the plasma-membrane glycerol and arsenite transporter, Fps1. Hog1 and Fps1 control the response to osmotic stress in yeast by regulating glycerol production and plasma membrane flux, respectively. We therefore tested whether APL cells have impaired osmoregulation. The APL cell line NB4 did not produce glycerol in response to osmotic stress and underwent apoptotic cell death. Moreover, the glycerol content of NB4 and differentiated NB4 cells correlated with the level of arsenic trioxide uptake and the sensitivity of the cells. Additionally, NB4 cells accumulated more arsenic trioxide than non-APL cells and were more sensitive. These findings demonstrate the usefulness of the S. cerevisiae deletion set and show that the selectivity of arsenic trioxide for APL cells relates, at least in part, to impaired osmoregulation and control of uptake of the drug.

Research paper thumbnail of The Phosphatidylinositol 3′-kinase p85α Gene Is an Oncogene in Human Ovarian and Colon Tumors

Cancer Research, Oct 15, 2001

Phosphatidylinositol 3-kinases (PI3ks) are a family of lipid kinases that play a crucial role in ... more Phosphatidylinositol 3-kinases (PI3ks) are a family of lipid kinases that play a crucial role in a wide range of important cellular processes associated with malignant behavior including cell growth, migration, and survival. We have used single-strand conformational polymorphism/ heteroduplex analysis to demonstrate the presence of somatic mutations in the gene for the p85␣ regulatory subunit of PI3k (PIK3R1) in primary human colon and ovarian tumors and cancer cell lines. All of the mutations lead to deletions in the inter-SH2 region of the molecule proximal to the serine 608 autoregulatory site. Expression of a mutant protein with a 23 amino acid deletion leads to constitutive activation of PI3k providing the first direct evidence that p85␣ is a new oncogene involved in human tumorigenesis. . The abbreviations used are: PI3k, phosphatidylinositol 3Ј-kinase; GFP, green fluorescent protein; SSCP/HD, single-strand conformational polymorphism/heteroduplex; nt, nucleotides; FBS, fetal bovine serum.

Research paper thumbnail of Microsatellite instability in gastrointestinal tract tumours

International journal of surgical investigation

Although a number of studies have documented microsatellite instability (MSI) in gastrointestinal... more Although a number of studies have documented microsatellite instability (MSI) in gastrointestinal tumours, the clinical significance is uncertain. In this study the MSI status and clinicopathological features were examined in gastric and colorectal tumours. Eighty-four gastrointestinal tumours were examined for MSI. Normal and tumour DNA isolated from the same patients were analysed at five different microsatellite loci. Clinical features of these patients were also collated and compared with MSI status. High level MSI (MSI-H) (as defined by instability in 2 or more microsatellites) was detected in 6 out of 47 (13%) colon tumours and 6 of 37 (16%) gastric tumours. The frequency of MSI-H between these groups was not statistically significant (P = 0.36). There was no significant correlation with patient age or gender, UICC stage, or degree of differentiation of the tumour. This was true both when analysed as a group, as well as when divided into colon and gastric sites. Our results co...

Research paper thumbnail of The phosphatidylinositol 3'-kinase p85alpha gene is an oncogene in human ovarian and colon tumors

Cancer research, Jan 15, 2001

Phosphatidylinositol 3'-kinases (PI3ks) are a family of lipid kinases that play a crucial rol... more Phosphatidylinositol 3'-kinases (PI3ks) are a family of lipid kinases that play a crucial role in a wide range of important cellular processes associated with malignant behavior including cell growth, migration, and survival. We have used single-strand conformational polymorphism/heteroduplex analysis to demonstrate the presence of somatic mutations in the gene for the p85alpha regulatory subunit of PI3k (PIK3R1) in primary human colon and ovarian tumors and cancer cell lines. All of the mutations lead to deletions in the inter-SH2 region of the molecule proximal to the serine608 autoregulatory site. Expression of a mutant protein with a 23 amino acid deletion leads to constitutive activation of PI3k providing the first direct evidence that p85alpha is a new oncogene involved in human tumorigenesis.

Research paper thumbnail of The Phosphatidylinositol 3-kinase p85 Gene Is an Oncogene in Human Ovarian and Colon Tumors1

Phosphatidylinositol 3-kinases (PI3ks) are a family of lipid kinases that play a crucial role in ... more Phosphatidylinositol 3-kinases (PI3ks) are a family of lipid kinases that play a crucial role in a wide range of important cellular processes asso- ciated with malignant behavior including cell growth, migration, and survival. We have used single-strand conformational polymorphism/ heteroduplex analysis to demonstrate the presence of somatic mutations in the gene for the p85 regulatory subunit of PI3k (PIK3R1) in

Research paper thumbnail of Insight into the selectivity of arsenic trioxide for acute promyelocytic leukemia cells by characterizing Saccharomyces cerevisiae deletion strains that are sensitive or resistant to the metalloid

The International Journal of Biochemistry & Cell Biology, 2008

The genome-wide set of Saccharomyces cerevisiae deletion strains provides the opportunity to anal... more The genome-wide set of Saccharomyces cerevisiae deletion strains provides the opportunity to analyze how other organisms may respond to toxic agents. Since arsenic trioxide selectively kills human acute promyelocytic leukemia (APL) cells by a poorly understood mechanism we screened the yeast deletion strains for sensitivity or resistance. In addition to confirming mutants previously identified as sensitive to sodium arsenite, a large number of additional genes, and cellular processes, were required for arsenic trioxide tolerance. Of the 4546 mutants, 7.6% were more sensitive to arsenic trioxide than the wild type, while 1.5% was more resistant. IC 50 values for all sensitive and resistant mutants were determined. Prominent as sensitive was that missing the MAP kinase, Hog1. The most resistant lacked the plasma-membrane glycerol and arsenite transporter, Fps1. Hog1 and Fps1 control the response to osmotic stress in yeast by regulating glycerol production and plasma membrane flux, respectively. We therefore tested whether APL cells have impaired osmoregulation. The APL cell line NB4 did not produce glycerol in response to osmotic stress and underwent apoptotic cell death. Moreover, the glycerol content of NB4 and differentiated NB4 cells correlated with the level of arsenic trioxide uptake and the sensitivity of the cells. Additionally, NB4 cells accumulated more arsenic trioxide than non-APL cells and were more sensitive. These findings demonstrate the usefulness of the S. cerevisiae deletion set and show that the selectivity of arsenic trioxide for APL cells relates, at least in part, to impaired osmoregulation and control of uptake of the drug.

Research paper thumbnail of The Saccharomyces cerevisiae orthologue of the human protein phosphatase 4 core regulatory subunit R2 confers resistance to the anticancer drug cisplatin

FEBS Journal, 2006

The anticancer agents cisplatin and oxaliplatin are widely used in the treatment of human neoplas... more The anticancer agents cisplatin and oxaliplatin are widely used in the treatment of human neoplasias. A genome-wide screen in Saccharomyces cerevisiae previously identified PPH3 and PSY2 among the top 20 genes conferring resistance to these anticancer agents. The mammalian orthologue of Pph3p is the protein serine/threonine phosphatase Ppp4c, which is found in high molecular mass complexes bound to a regulatory subunit R2. We show here that the putative S. cerevisiae orthologue of R2, which is encoded by ORF YBL046w, binds to Pph3p and exhibits the same unusually high asymmetry as mammalian R2. Despite the essential function of Ppp4c-R2 in microtubule-related processes at centrosomes in higher eukaryotes, S. cerevisiae diploid strains with homozygous deletion of YBL046w and two or one functional copies of the TUB2 gene were viable and no more sensitive to microtubule-depolymerizing drugs than the control strain. The protein encoded by YBL046w exhibited a predominantly nuclear localization. These studies suggest that the centrosomal function of Ppp4c-R2 is not required or may be performed by a different phosphatase in yeast. Homozygous diploid deletion strains of S. cerevisiae, pph3Delta, ybl046wDelta and psy2Delta, were all more sensitive to cisplatin than the control strain. The YBL046w gene therefore confers resistance to cisplatin and was termed PSY4 (platinum sensitivity 4). Ppp4c, R2 and the putative orthologue of Psy2p (termed R3) are shown here to form a complex in Drosophila melanogaster and mammalian cells. By comparison with the yeast system, this complex may confer resistance to cisplatin in higher eukaryotes.

Research paper thumbnail of Protein phosphatase 4 interacts with the Survival of Motor Neurons complex and enhances the temporal localisation of snRNPs

Journal of Cell Science, 2003

Research paper thumbnail of Protein phosphatase 4 – from obscurity to vital functions

FEBS Letters, 2005

Protein phosphatase 4 (Ppp4) is a ubiquitous serine/ threonine phosphatase in the PPP family that... more Protein phosphatase 4 (Ppp4) is a ubiquitous serine/ threonine phosphatase in the PPP family that is now recognised to regulate a variety of cellular functions independently of protein phosphatase 2A (PP2A). Regulatory subunits (R1 and R2) have been identified in mammals that interact with the catalytic subunit of Ppp4 (Ppp4c) and control its activity. Ppp4c-R2 complexes play roles in organelle assembly; not only are they essential for maturation of the centrosome, but they are also involved in spliceosomal assembly via interaction with the survival of motor neurons (SMNs) complex. Several cellular signalling routes, including NF-jB and the target of rapamycin (TOR) pathways appear to be regulated by Ppp4. Emerging evidence indicates that Ppp4 may play a role in the DNA damage response and that Ppp4c-R1 complexes decrease the activity of a histone deacetylase, implicating Ppp4 in the regulation of chromatin activities. Antitumour agents, cantharidin and fostriecin, potently inhibit the activity of Ppp4. Orthologues of mammalian Ppp4 subunits in Saccharomyces cerevisiae confer resistance to the anticancer, DNA-binding drugs, cisplatin and oxaliplatin.

Research paper thumbnail of Depletion of protein phosphatase 4 in human cells reveals essential roles in centrosome maturation, cell migration and the regulation of Rho GTPases

The International Journal of Biochemistry & Cell Biology, 2008

The mechanisms that co-ordinate centrosome maturation and the migration of human cells remain elu... more The mechanisms that co-ordinate centrosome maturation and the migration of human cells remain elusive. Protein phosphatase 4 (Ppp4) is a ubiquitous protein serine/threonine phosphatase in eukaryotes that is enriched at centrosomes. HEK293 cells cultures depleted to 30% Ppp4c levels by lentivirus-delivered stable gene silencing were delayed in mitosis at the prometaphase/metaphase boundary and displayed cells with aberrant chromosome organisation and microtubules unconnected to the centrosomes. The levels of ␣and ␥-tubulin and aurora A were decreased; in mitotic cells, the cytological localisations of polo-like kinase 1, ␣and ␥-tubulin and aurora A were aberrant and the phosphorylation of Aurora A-Thr 288 was decreased. The novel localisation of endogenous Ppp4 regulatory subunit, R3A, to centrosomes in human mitotic cells suggests that a Ppp4c-R2-R3 trimeric complex mediates centrosome maturation. We demonstrate for the first time that human cells depleted to 30% Ppp4c showed severely decreased migration and exhibit decreased levels of both total ␤-actin and filamentous actin in cell extensions, filopodia and lamellopodia-like structures. Our studies show that Ppp4c is required for the organisation of the actin cytoskeleton at the leading edge of human cells during migration. We also demonstrate that the active forms of the RhoGTPases, Rac1 and Cdc42, are substantially decreased in the presence and absence of growth factor in Ppp4c depleted cells, implicating Ppp4c in the regulation of these GTPases. The results suggest that Ppp4c-R2-R3 complexes may co-ordinate centrosome maturation and cell migration via regulation of RhoGTPases and that Ppp4 may be a useful anticancer target.

Research paper thumbnail of Indigenous Health: ACTION on Prevention - 50th annual Australian Society for Medical Research National Scientific Conference

Rural and Remote Health, Jul 1, 2012

The 50th annual National Scientific Conference of the Australian Society for Medical Research was... more The 50th annual National Scientific Conference of the Australian Society for Medical Research was held in Cairns, Queensland, 13-16 November 2011. The theme, 'Indigenous Health: ACTION on Prevention' highlighted the direct action being undertaken by health and medical researchers, as well as allied health professionals, to improve long-term health outcomes for Indigenous Australians.

Research paper thumbnail of Insight into the selectivity of arsenic trioxide for acute promyelocytic leukemia cells by characterizing Saccharomyces cerevisiae deletion strains that are sensitive or resistant to the metalloid

The International Journal of Biochemistry Cell Biology, Feb 1, 2008

The genome-wide set of Saccharomyces cerevisiae deletion strains provides the opportunity to anal... more The genome-wide set of Saccharomyces cerevisiae deletion strains provides the opportunity to analyze how other organisms may respond to toxic agents. Since arsenic trioxide selectively kills human acute promyelocytic leukemia (APL) cells by a poorly understood mechanism we screened the yeast deletion strains for sensitivity or resistance. In addition to confirming mutants previously identified as sensitive to sodium arsenite, a large number of additional genes, and cellular processes, were required for arsenic trioxide tolerance. Of the 4546 mutants, 7.6% were more sensitive to arsenic trioxide than the wild type, while 1.5% was more resistant. IC 50 values for all sensitive and resistant mutants were determined. Prominent as sensitive was that missing the MAP kinase, Hog1. The most resistant lacked the plasma-membrane glycerol and arsenite transporter, Fps1. Hog1 and Fps1 control the response to osmotic stress in yeast by regulating glycerol production and plasma membrane flux, respectively. We therefore tested whether APL cells have impaired osmoregulation. The APL cell line NB4 did not produce glycerol in response to osmotic stress and underwent apoptotic cell death. Moreover, the glycerol content of NB4 and differentiated NB4 cells correlated with the level of arsenic trioxide uptake and the sensitivity of the cells. Additionally, NB4 cells accumulated more arsenic trioxide than non-APL cells and were more sensitive. These findings demonstrate the usefulness of the S. cerevisiae deletion set and show that the selectivity of arsenic trioxide for APL cells relates, at least in part, to impaired osmoregulation and control of uptake of the drug.

Research paper thumbnail of The Phosphatidylinositol 3′-kinase p85α Gene Is an Oncogene in Human Ovarian and Colon Tumors

Cancer Research, Oct 15, 2001

Phosphatidylinositol 3-kinases (PI3ks) are a family of lipid kinases that play a crucial role in ... more Phosphatidylinositol 3-kinases (PI3ks) are a family of lipid kinases that play a crucial role in a wide range of important cellular processes associated with malignant behavior including cell growth, migration, and survival. We have used single-strand conformational polymorphism/ heteroduplex analysis to demonstrate the presence of somatic mutations in the gene for the p85␣ regulatory subunit of PI3k (PIK3R1) in primary human colon and ovarian tumors and cancer cell lines. All of the mutations lead to deletions in the inter-SH2 region of the molecule proximal to the serine 608 autoregulatory site. Expression of a mutant protein with a 23 amino acid deletion leads to constitutive activation of PI3k providing the first direct evidence that p85␣ is a new oncogene involved in human tumorigenesis. . The abbreviations used are: PI3k, phosphatidylinositol 3Ј-kinase; GFP, green fluorescent protein; SSCP/HD, single-strand conformational polymorphism/heteroduplex; nt, nucleotides; FBS, fetal bovine serum.

Research paper thumbnail of Microsatellite instability in gastrointestinal tract tumours

International journal of surgical investigation

Although a number of studies have documented microsatellite instability (MSI) in gastrointestinal... more Although a number of studies have documented microsatellite instability (MSI) in gastrointestinal tumours, the clinical significance is uncertain. In this study the MSI status and clinicopathological features were examined in gastric and colorectal tumours. Eighty-four gastrointestinal tumours were examined for MSI. Normal and tumour DNA isolated from the same patients were analysed at five different microsatellite loci. Clinical features of these patients were also collated and compared with MSI status. High level MSI (MSI-H) (as defined by instability in 2 or more microsatellites) was detected in 6 out of 47 (13%) colon tumours and 6 of 37 (16%) gastric tumours. The frequency of MSI-H between these groups was not statistically significant (P = 0.36). There was no significant correlation with patient age or gender, UICC stage, or degree of differentiation of the tumour. This was true both when analysed as a group, as well as when divided into colon and gastric sites. Our results co...

Research paper thumbnail of The phosphatidylinositol 3'-kinase p85alpha gene is an oncogene in human ovarian and colon tumors

Cancer research, Jan 15, 2001

Phosphatidylinositol 3'-kinases (PI3ks) are a family of lipid kinases that play a crucial rol... more Phosphatidylinositol 3'-kinases (PI3ks) are a family of lipid kinases that play a crucial role in a wide range of important cellular processes associated with malignant behavior including cell growth, migration, and survival. We have used single-strand conformational polymorphism/heteroduplex analysis to demonstrate the presence of somatic mutations in the gene for the p85alpha regulatory subunit of PI3k (PIK3R1) in primary human colon and ovarian tumors and cancer cell lines. All of the mutations lead to deletions in the inter-SH2 region of the molecule proximal to the serine608 autoregulatory site. Expression of a mutant protein with a 23 amino acid deletion leads to constitutive activation of PI3k providing the first direct evidence that p85alpha is a new oncogene involved in human tumorigenesis.

Research paper thumbnail of The Phosphatidylinositol 3-kinase p85 Gene Is an Oncogene in Human Ovarian and Colon Tumors1

Phosphatidylinositol 3-kinases (PI3ks) are a family of lipid kinases that play a crucial role in ... more Phosphatidylinositol 3-kinases (PI3ks) are a family of lipid kinases that play a crucial role in a wide range of important cellular processes asso- ciated with malignant behavior including cell growth, migration, and survival. We have used single-strand conformational polymorphism/ heteroduplex analysis to demonstrate the presence of somatic mutations in the gene for the p85 regulatory subunit of PI3k (PIK3R1) in

Research paper thumbnail of Insight into the selectivity of arsenic trioxide for acute promyelocytic leukemia cells by characterizing Saccharomyces cerevisiae deletion strains that are sensitive or resistant to the metalloid

The International Journal of Biochemistry & Cell Biology, 2008

The genome-wide set of Saccharomyces cerevisiae deletion strains provides the opportunity to anal... more The genome-wide set of Saccharomyces cerevisiae deletion strains provides the opportunity to analyze how other organisms may respond to toxic agents. Since arsenic trioxide selectively kills human acute promyelocytic leukemia (APL) cells by a poorly understood mechanism we screened the yeast deletion strains for sensitivity or resistance. In addition to confirming mutants previously identified as sensitive to sodium arsenite, a large number of additional genes, and cellular processes, were required for arsenic trioxide tolerance. Of the 4546 mutants, 7.6% were more sensitive to arsenic trioxide than the wild type, while 1.5% was more resistant. IC 50 values for all sensitive and resistant mutants were determined. Prominent as sensitive was that missing the MAP kinase, Hog1. The most resistant lacked the plasma-membrane glycerol and arsenite transporter, Fps1. Hog1 and Fps1 control the response to osmotic stress in yeast by regulating glycerol production and plasma membrane flux, respectively. We therefore tested whether APL cells have impaired osmoregulation. The APL cell line NB4 did not produce glycerol in response to osmotic stress and underwent apoptotic cell death. Moreover, the glycerol content of NB4 and differentiated NB4 cells correlated with the level of arsenic trioxide uptake and the sensitivity of the cells. Additionally, NB4 cells accumulated more arsenic trioxide than non-APL cells and were more sensitive. These findings demonstrate the usefulness of the S. cerevisiae deletion set and show that the selectivity of arsenic trioxide for APL cells relates, at least in part, to impaired osmoregulation and control of uptake of the drug.

Research paper thumbnail of The Saccharomyces cerevisiae orthologue of the human protein phosphatase 4 core regulatory subunit R2 confers resistance to the anticancer drug cisplatin

FEBS Journal, 2006

The anticancer agents cisplatin and oxaliplatin are widely used in the treatment of human neoplas... more The anticancer agents cisplatin and oxaliplatin are widely used in the treatment of human neoplasias. A genome-wide screen in Saccharomyces cerevisiae previously identified PPH3 and PSY2 among the top 20 genes conferring resistance to these anticancer agents. The mammalian orthologue of Pph3p is the protein serine/threonine phosphatase Ppp4c, which is found in high molecular mass complexes bound to a regulatory subunit R2. We show here that the putative S. cerevisiae orthologue of R2, which is encoded by ORF YBL046w, binds to Pph3p and exhibits the same unusually high asymmetry as mammalian R2. Despite the essential function of Ppp4c-R2 in microtubule-related processes at centrosomes in higher eukaryotes, S. cerevisiae diploid strains with homozygous deletion of YBL046w and two or one functional copies of the TUB2 gene were viable and no more sensitive to microtubule-depolymerizing drugs than the control strain. The protein encoded by YBL046w exhibited a predominantly nuclear localization. These studies suggest that the centrosomal function of Ppp4c-R2 is not required or may be performed by a different phosphatase in yeast. Homozygous diploid deletion strains of S. cerevisiae, pph3Delta, ybl046wDelta and psy2Delta, were all more sensitive to cisplatin than the control strain. The YBL046w gene therefore confers resistance to cisplatin and was termed PSY4 (platinum sensitivity 4). Ppp4c, R2 and the putative orthologue of Psy2p (termed R3) are shown here to form a complex in Drosophila melanogaster and mammalian cells. By comparison with the yeast system, this complex may confer resistance to cisplatin in higher eukaryotes.

Research paper thumbnail of Protein phosphatase 4 interacts with the Survival of Motor Neurons complex and enhances the temporal localisation of snRNPs

Journal of Cell Science, 2003

Research paper thumbnail of Protein phosphatase 4 – from obscurity to vital functions

FEBS Letters, 2005

Protein phosphatase 4 (Ppp4) is a ubiquitous serine/ threonine phosphatase in the PPP family that... more Protein phosphatase 4 (Ppp4) is a ubiquitous serine/ threonine phosphatase in the PPP family that is now recognised to regulate a variety of cellular functions independently of protein phosphatase 2A (PP2A). Regulatory subunits (R1 and R2) have been identified in mammals that interact with the catalytic subunit of Ppp4 (Ppp4c) and control its activity. Ppp4c-R2 complexes play roles in organelle assembly; not only are they essential for maturation of the centrosome, but they are also involved in spliceosomal assembly via interaction with the survival of motor neurons (SMNs) complex. Several cellular signalling routes, including NF-jB and the target of rapamycin (TOR) pathways appear to be regulated by Ppp4. Emerging evidence indicates that Ppp4 may play a role in the DNA damage response and that Ppp4c-R1 complexes decrease the activity of a histone deacetylase, implicating Ppp4 in the regulation of chromatin activities. Antitumour agents, cantharidin and fostriecin, potently inhibit the activity of Ppp4. Orthologues of mammalian Ppp4 subunits in Saccharomyces cerevisiae confer resistance to the anticancer, DNA-binding drugs, cisplatin and oxaliplatin.

Research paper thumbnail of Depletion of protein phosphatase 4 in human cells reveals essential roles in centrosome maturation, cell migration and the regulation of Rho GTPases

The International Journal of Biochemistry & Cell Biology, 2008

The mechanisms that co-ordinate centrosome maturation and the migration of human cells remain elu... more The mechanisms that co-ordinate centrosome maturation and the migration of human cells remain elusive. Protein phosphatase 4 (Ppp4) is a ubiquitous protein serine/threonine phosphatase in eukaryotes that is enriched at centrosomes. HEK293 cells cultures depleted to 30% Ppp4c levels by lentivirus-delivered stable gene silencing were delayed in mitosis at the prometaphase/metaphase boundary and displayed cells with aberrant chromosome organisation and microtubules unconnected to the centrosomes. The levels of ␣and ␥-tubulin and aurora A were decreased; in mitotic cells, the cytological localisations of polo-like kinase 1, ␣and ␥-tubulin and aurora A were aberrant and the phosphorylation of Aurora A-Thr 288 was decreased. The novel localisation of endogenous Ppp4 regulatory subunit, R3A, to centrosomes in human mitotic cells suggests that a Ppp4c-R2-R3 trimeric complex mediates centrosome maturation. We demonstrate for the first time that human cells depleted to 30% Ppp4c showed severely decreased migration and exhibit decreased levels of both total ␤-actin and filamentous actin in cell extensions, filopodia and lamellopodia-like structures. Our studies show that Ppp4c is required for the organisation of the actin cytoskeleton at the leading edge of human cells during migration. We also demonstrate that the active forms of the RhoGTPases, Rac1 and Cdc42, are substantially decreased in the presence and absence of growth factor in Ppp4c depleted cells, implicating Ppp4c in the regulation of these GTPases. The results suggest that Ppp4c-R2-R3 complexes may co-ordinate centrosome maturation and cell migration via regulation of RhoGTPases and that Ppp4 may be a useful anticancer target.