Miriam Falzon - Academia.edu (original) (raw)

Papers by Miriam Falzon

Regulatory Peptides, 2009

Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell li... more Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell lines; expression correlates with colon carcinoma severity. PTHrP is synthesized as a prepro isoform and contains two targeting sequences-a signal sequence and a nuclear localization signal (NLS). The signal peptide (SP) directs PTHrP to the secretory pathway, where it exerts autocrine/paracrine effects. The NLS directs PTHrP to the nucleus/nucleolus, where it exerts intracrine effects. In this study, we used the human colon cancer cell line LoVo as a model system to study the effects of autocrine/paracrine and intracrine PTHrP action on cell growth and survival, hallmarks of malignant tumor cells. We report that PTHrP increases cell growth and survival, protects cells from serumstarvation-induced apoptosis, and promotes anchorage-independent cell growth via an intracrine pathway. Conversely, autocrine/paracrine PTHrP action decreases cell growth and survival. We also show an inverse relationship between secreted and nuclear PTHrP levels, in that cells overexpressing NLS-deleted PTHrP secrete higher PTHrP levels than those overexpressing the wild-type isoform. Conversely, SP deletion results in higher nuclear PTHrP levels. These observations provide evidence of a link between intracrine PTHrP action and cell growth and survival. Targeting PTHrP production in colon cancer may thus prove therapeutically beneficial.

Steroids, 2007

Parathyroid hormone-related protein (PTHrP) increases the growth and metastatic potential of pros... more Parathyroid hormone-related protein (PTHrP) increases the growth and metastatic potential of prostate cancer cells, making it important to control PTHrP expression in these cells. 1,25-Dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] suppresses PTHrP expression and exerts an anti-proliferative effect in prostate carcinoma cells. We used the human prostate cancer cell line C4-2 as a model system to ask whether down-regulation of PTHrP expression by 1,25(OH) 2 D 3 plays a role in the anti-proliferative effects of 1,25(OH) 2 D 3. Since PTHrP increases the expression of the pro-invasive integrin α6β4, we also asked whether 1,25(OH) 2 D 3 decreases integrin α6β4 expression in C4-2 cells, and whether modulation of PTHrP expression by 1,25(OH) 2 D 3 plays a role in the effects of 1,25 (OH) 2 D 3 on integrin α6β4 expression. Two strategies were utilized to modulate PTHrP levels: overexpression of PTHrP (−36 to +139) and suppression of endogenous PTHrP expression using siRNAs. We report a direct correlation between PTHrP expression, C4-2 cell proliferation, and integrin α6β4 expression at the mRNA and cell surface protein level. Treatment of parental C4-2 cells with 1,25(OH) 2 D 3 decreased cell proliferation and integrin α6 and β4 expression. These 1,25 (OH) 2 D 3 effects were significantly attenuated in cells with suppressed PTHrP expression. 1,25 (OH) 2 D 3 regulates PTHrP expression via a negative vitamin D response element (nVDRE) within the noncoding region of the PTHrP gene. The effects of 1,25(OH) 2 D 3 on cell proliferation and integrin α6β4 expression were significantly attenuated in cells overexpressing PTHrP (−36 to +139), which lacks the nVDRE. These findings suggest that one of the pathways via which 1,25(OH) 2 D 3 exerts its anti-proliferative effects is through down-regulation of PTHrP expression.

Lung Cancer, 1987

In the normal lungs of many animal species, 4-ipomeanol is trans formed to a highly reactive meta... more In the normal lungs of many animal species, 4-ipomeanol is trans formed to a highly reactive metabolite preferentially in pulmonary bronchiolar Clara cells and to a lesser extent in alveolar type II cells, potentially leading to damage or destruction of these cell types. Since Clara cells and type II cells are suspected sites of origin of certain "nonsmall ceir lung cancers, the metabolic activation of 4-ipomeanol (mea sured by the metabolism-dependent covalent binding of 4-ipomeanol to cellular macromolecules) was compared in two human non-small cell carcinoma derived cell lines (NCI-H322 and NCI-H358) and two human small cell carcinoma derived cell lines (Nil-Ill 28 and NCI-H69). Met abolic activation of 4-ipomeanol was evident in the non-small cell lines; the production of covalently bound metabolite was somewhat greater in NCI-H322 (morphology related to Clara cells) compared to NCI-H358 (morphology related to alveolar type II cells), but was entirely undetectable in the small cell lines. The activation pathway was concentration (4ipomeanol) and time dependent and followed Michaelis-Meuten kinetics. Metabolism to the reactive intermediate required oxygen and was strongly inhibited by carbon monoxide. Covalent binding was enhanced in the nonsmall cell lines by prior incubation with 0-naphthoflavone and by supple mentation of the incubate with exogenous reduced nicotinamide adenine dinucleotide phosphate. 4-Ipomeanol was more cytotoxic to the non-small cell lines than to the small cell lines under the in vitro growth conditions used. These studies indicate that certain human non-small cell lung cancers have metabolic characteristics of normal bronchiolar Clara cells and alveolar type II cells; these results would therefore be consistent with an origin of these tumors from Clara cells or type II cells, respec tively. The present studies indicate that the further preclinical testing and development of 4-ipomeanol is warranted, with a view toward possible clinical evaluation against human lung cancers.

Cancer Letters, 2010

Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell li... more Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell lines. Rac1 GTPase enhances colon cancer cell migration and invasion. Here we report a positive correlation between PTHrP expression and Rac1 activity in LoVo (human colon cancer) cells. The positive effects of PTHrP on Rac1 activity and on cell migration and invasion are mediated via the guanine nucleotide exchange factor Tiam1. Knockdown of integrin α6β4, which is upregulated by PTHrP, negates the PTHrP-mediated increase in Rac1 activation. Integrin α6β4 signals synergistically with growth factor receptors to activate the phosphatidylinositol 3-kinase (PI3-K) pathway. Chemical inhibition of PI3-K negates the PTHrP-mediated effects on Tiam1 and Rac1 activity. Tumors from PTHrP-overexpressing LoVo cells also show increased expression of Tiam1. Taken together, these observations provide evidence of a link between PTHrP and Rac1 activity through integrin α6β4, resulting in enhanced cell migration and invasion. Targeting PTHrP production in colon cancer may thus prove therapeutically beneficial.

Regulatory Peptides, 2009

Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell li... more Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell lines; expression correlates with colon carcinoma severity. PTHrP is synthesized as a prepro isoform and contains two targeting sequences-a signal sequence and a nuclear localization signal (NLS). The signal peptide (SP) directs PTHrP to the secretory pathway, where it exerts autocrine/paracrine effects. The NLS directs PTHrP to the nucleus/nucleolus, where it exerts intracrine effects. In this study, we used the human colon cancer cell line LoVo as a model system to study the effects of autocrine/paracrine and intracrine PTHrP action on cell growth and survival, hallmarks of malignant tumor cells. We report that PTHrP increases cell growth and survival, protects cells from serumstarvation-induced apoptosis, and promotes anchorage-independent cell growth via an intracrine pathway. Conversely, autocrine/paracrine PTHrP action decreases cell growth and survival. We also show an inverse relationship between secreted and nuclear PTHrP levels, in that cells overexpressing NLS-deleted PTHrP secrete higher PTHrP levels than those overexpressing the wild-type isoform. Conversely, SP deletion results in higher nuclear PTHrP levels. These observations provide evidence of a link between intracrine PTHrP action and cell growth and survival. Targeting PTHrP production in colon cancer may thus prove therapeutically beneficial.

Steroids, 2007

Parathyroid hormone-related protein (PTHrP) increases the growth and metastatic potential of pros... more Parathyroid hormone-related protein (PTHrP) increases the growth and metastatic potential of prostate cancer cells, making it important to control PTHrP expression in these cells. 1,25-Dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] suppresses PTHrP expression and exerts an anti-proliferative effect in prostate carcinoma cells. We used the human prostate cancer cell line C4-2 as a model system to ask whether down-regulation of PTHrP expression by 1,25(OH) 2 D 3 plays a role in the anti-proliferative effects of 1,25(OH) 2 D 3. Since PTHrP increases the expression of the pro-invasive integrin α6β4, we also asked whether 1,25(OH) 2 D 3 decreases integrin α6β4 expression in C4-2 cells, and whether modulation of PTHrP expression by 1,25(OH) 2 D 3 plays a role in the effects of 1,25 (OH) 2 D 3 on integrin α6β4 expression. Two strategies were utilized to modulate PTHrP levels: overexpression of PTHrP (−36 to +139) and suppression of endogenous PTHrP expression using siRNAs. We report a direct correlation between PTHrP expression, C4-2 cell proliferation, and integrin α6β4 expression at the mRNA and cell surface protein level. Treatment of parental C4-2 cells with 1,25(OH) 2 D 3 decreased cell proliferation and integrin α6 and β4 expression. These 1,25 (OH) 2 D 3 effects were significantly attenuated in cells with suppressed PTHrP expression. 1,25 (OH) 2 D 3 regulates PTHrP expression via a negative vitamin D response element (nVDRE) within the noncoding region of the PTHrP gene. The effects of 1,25(OH) 2 D 3 on cell proliferation and integrin α6β4 expression were significantly attenuated in cells overexpressing PTHrP (−36 to +139), which lacks the nVDRE. These findings suggest that one of the pathways via which 1,25(OH) 2 D 3 exerts its anti-proliferative effects is through down-regulation of PTHrP expression.

Lung Cancer, 1987

In the normal lungs of many animal species, 4-ipomeanol is trans formed to a highly reactive meta... more In the normal lungs of many animal species, 4-ipomeanol is trans formed to a highly reactive metabolite preferentially in pulmonary bronchiolar Clara cells and to a lesser extent in alveolar type II cells, potentially leading to damage or destruction of these cell types. Since Clara cells and type II cells are suspected sites of origin of certain "nonsmall ceir lung cancers, the metabolic activation of 4-ipomeanol (mea sured by the metabolism-dependent covalent binding of 4-ipomeanol to cellular macromolecules) was compared in two human non-small cell carcinoma derived cell lines (NCI-H322 and NCI-H358) and two human small cell carcinoma derived cell lines (Nil-Ill 28 and NCI-H69). Met abolic activation of 4-ipomeanol was evident in the non-small cell lines; the production of covalently bound metabolite was somewhat greater in NCI-H322 (morphology related to Clara cells) compared to NCI-H358 (morphology related to alveolar type II cells), but was entirely undetectable in the small cell lines. The activation pathway was concentration (4ipomeanol) and time dependent and followed Michaelis-Meuten kinetics. Metabolism to the reactive intermediate required oxygen and was strongly inhibited by carbon monoxide. Covalent binding was enhanced in the nonsmall cell lines by prior incubation with 0-naphthoflavone and by supple mentation of the incubate with exogenous reduced nicotinamide adenine dinucleotide phosphate. 4-Ipomeanol was more cytotoxic to the non-small cell lines than to the small cell lines under the in vitro growth conditions used. These studies indicate that certain human non-small cell lung cancers have metabolic characteristics of normal bronchiolar Clara cells and alveolar type II cells; these results would therefore be consistent with an origin of these tumors from Clara cells or type II cells, respec tively. The present studies indicate that the further preclinical testing and development of 4-ipomeanol is warranted, with a view toward possible clinical evaluation against human lung cancers.

Cancer Letters, 2010

Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell li... more Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell lines. Rac1 GTPase enhances colon cancer cell migration and invasion. Here we report a positive correlation between PTHrP expression and Rac1 activity in LoVo (human colon cancer) cells. The positive effects of PTHrP on Rac1 activity and on cell migration and invasion are mediated via the guanine nucleotide exchange factor Tiam1. Knockdown of integrin α6β4, which is upregulated by PTHrP, negates the PTHrP-mediated increase in Rac1 activation. Integrin α6β4 signals synergistically with growth factor receptors to activate the phosphatidylinositol 3-kinase (PI3-K) pathway. Chemical inhibition of PI3-K negates the PTHrP-mediated effects on Tiam1 and Rac1 activity. Tumors from PTHrP-overexpressing LoVo cells also show increased expression of Tiam1. Taken together, these observations provide evidence of a link between PTHrP and Rac1 activity through integrin α6β4, resulting in enhanced cell migration and invasion. Targeting PTHrP production in colon cancer may thus prove therapeutically beneficial.