SRC-family kinases are activated in non-small cell lung cancer and promote the survival of epidermal growth factor receptor-dependent cell lines - PubMed (original) (raw)

SRC-family kinases are activated in non-small cell lung cancer and promote the survival of epidermal growth factor receptor-dependent cell lines

Jie Zhang et al. Am J Pathol. 2007 Jan.

Abstract

The role of Src-family kinases (SFKs) in non-small cell lung cancer (NSCLC) has not been fully defined. Here we addressed this question by examining SFK phosphorylation in NSCLC biopsy samples and using genetic and pharmacological approaches to inhibit SFK expression and activity in cultured NSCLC cells. Immunohistochemical analysis of NSCLC biopsy samples using a Tyr416 phosphorylation-specific, pan-SFK antibody revealed staining in 123 (33%) of 370 tumors. Because c-Src is known to be both an upstream activator and downstream mediator of epidermal growth factor receptor (EGFR), we next investigated SFK phosphorylation in a panel of NSCLC cell lines, including ones that depend on EGFR for survival. The EGFR-dependent NSCLC cell lines HCC827 and H3255 had increased phosphorylation of SFKs, and treatment of these cells with an SFK inhibitor (PP1 or SKI-606) induced apoptosis. PP1 decreased phosphorylation of EGFR, ErbB2, and ErbB3 and strikingly enhanced apoptosis by gefitinib, an EGFR inhibitor. HCC827 cells transfected with c-Src short hairpin RNA exhibited diminished phosphorylation of EGFR and ErbB2 and decreased sensitivity to apoptosis by PP1 or gefitinib. We conclude that SFKs are activated in NSCLC biopsy samples, promote the survival of EGFR-dependent NSCLC cells, and should be investigated as therapeutic targets in NSCLC patients.

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Figures

Figure 1

Figure 1

SFK Tyr416 phosphorylation in NSCLC biopsy samples. A: Western blotting of H1299 cells stably transfected with dominant active mutant c-Src (DA-Src) or empty vector (H1299). B: Optimization of P-SFK immunohistochemical staining conditions so that staining was absent without primary antibody (10 Ab) or in the presence of blocking peptide (peptide). C: Examples of tumors staining positively for P-SFK (ADC, adenocarcinoma; SCC, squamous cell carcinoma; BAC, bronchioloalveolar cell carcinoma). D: Example of bronchial epithelial staining positively for P-SFK. Arrow points to a positive cell in basal layer.

Figure 2

Figure 2

Increased SFK phosphorylation in EGFR-dependent NSCLC cell lines. A: Western blotting of P-SFK and total SFKs in NSCLC cell lines. Actin was used as a loading control. B: Serum withdrawal enhanced SFK phosphorylation in EGFR-dependent cell lines. Western analysis of NSCLC cell lines in the presence of serum (+SFK) or subjected to serum withdrawal for 48 hours (−SFK). C: SFK phosphorylation increased in a time-dependent manner after serum withdrawal. Western analysis of HCC827 cells lysed before (t = 0) or at the indicated time points after serum withdrawal. Actin was used as a loading control.

Figure 3

Figure 3

SFKs are required for the survival of EGFR-dependent NSCLC cells. Western blotting of NSCLC cell lines treated with PP1. A: WST-1 assays of NSCLC cells treated with PP1 or SKI-606. Values expressed relative to control cells treated with DMSO, which were set at 1. B and C: Western blotting of NSCLC cells treated with PP1 (10 μmol/L), SKI-606 (2 μmol/L), or vehicle (C). SFK inhibition was assessed by detection of P-SFK and apoptosis by caspase-3 and PARP cleavage. Actin was used as a loading control.

Figure 4

Figure 4

c-Src depletion in HCC827 cells diminishes sensitivity to PP1. A: Western blotting of HCC827 cells stably transfected with Src shRNA vectors (A, C, or D), empty vector (vector), or nothing (HCC827). B: WST-1 assays to examine the proliferation of transfectants (shRNA or pRS empty vector) and parental cells (HCC827) treated with PP1. Values for shRNA transfectants were expressed relative to values for parental cells (HCC827) treated with DMSO, which were set at 1. As an additional control, we compared parental cells and pRS transfectants with respect to effects of PP1, which were indistinguishable in these cells (top left).

Figure 5

Figure 5

SFKs regulate phosphorylation of EGFR, ErbB2, and ErbB3. A: Western analysis of ErbB family members in NSCLC cell lines treated with PP1. Actin was used as a loading control. B: Western blotting of HCC827 cells stably transfected with Src shRNA vectors (A, C, or D), empty vector (vector), or nothing (HCC827).

Figure 6

Figure 6

PP1 and gefitinib have synergistic effects. A: WST-1 assays to examine the proliferation of HCC827 cells and H3255 cells treated with PP1, gefitinib, or both. Values were expressed relative to control cells treated with DMSO, which were set at 1. Apoptosis detected by TUNEL assay (B) and Western blotting of PARP and cleaved caspase-3 (C) in HCC827 cells treated with gefitinib (5 nmol/L), PP1 (1 μmol/L), both, or control (DMSO). Percentages of apoptotic cells detected by TUNEL are indicated (* = %). Actin was used as a loading control in C. D: Western blotting to examine effects of gefitinib, PP1, both, or neither, on downstream mediators of EGFR and SFKs in HCC827 cells. The intensities of the bands were quantified by densitometric analysis and normalized by total ERK, total STAT3, or actin (for cyclin D1). Phosphorylation levels were expressed relative to that of control cells treated with DMSO (Con), which were set at 1.

Figure 7

Figure 7

c-Src depletion in HCC827 cells diminishes sensitivity to gefitinib. WST-1 assays to examine the proliferation of transfectants (shRNA or pRS empty vector) and parental cells (HCC827) treated with gefitinib. Values for shRNA transfectants were expressed relative to values for parental cells (HCC827) treated with DMSO, which were set at 1. As an additional control, we compared parental cells and pRS transfectants with respect to effects of gefitinib, which were indistinguishable in these cells (top left).

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