Direct tumorigenic conversion of human gallbladder carcinoma cells by v-src but not by activated c-H-ras oncogene

Differential anti-tumor activities of curcumin against Ras- and Src-activated human adenocarcinoma cells

Although curcumin has been studied as a potential anticancer drug targeting multiple signaling molecules, the role of oncogenic Src and Ras in curcumin sensitivity remains unknown. Using HAG-1 human adenocarcinoma cells transfected with either activated Src or Ras, we investigated here the functional role of these oncogenes in curcumin sensitivity. Activation of either Src or Ras did not confer resistance to curcumin, compared to vehicle-transfected cells. Curcumin enhanced Erk1/2 predominantly in Ras-activated cells, but inhibited Akt and its downstream molecules (mTOR and S6K1) regardless of these oncogene activations. The sub-G0/G1 apoptotic populations were substantially increased with demonstrable cleavage of PARP, but this increase was most prominent in Src-activated cells. Suppression of Bcl-xL level and enhanced expression of Bax were demonstrated in Src-activated, but not Ras-activated cells. By contrast, drastic increases of G2/M cell populations were seen in Ras-activated cells rather than Src-activated cells, suggesting a potential role of Ras/Erk1/2 activation in curcumin-induced G2/M arrest. These data indicate that curcumin-induced growth inhibition would be mediated mainly by G2/M arrest in Ras-driven cells but by apoptosis induction in Src-driven cells, providing a mechanistic rationale for the potential use of curcumin in the treatment of human cancers with activated Src or Ras.

Activated Src and Ras induce gefitinib resistance by activation of signaling pathways downstream of epidermal growth factor receptor in human gallbladder adenocarcinoma cells

PURPOSE

Although gefitinib, a selective inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, has been demonstrated to exhibit its antitumor activity by the blockade of EGF receptor, the role of signaling pathways downstream of EGFR in gefitinib sensitivity remains unknown. In this study, we investigated the mechanistic role of Src and Ras, major oncogene products implicated in the pathogenesis of many human cancers in gefitinib sensitivity.

METHODS

Using parental and v-src- or c-H-ras-transfected HAG-1 human gallbladder adenocarcinoma cell lines, effects of gefitinib on cytotoxicity, cell cycle purtubation and apoptosis, and tyrosine phosphorylation of EGFR, Akt, and Erk were determined by WST-1 assay, flow cytometry, and Western blots, respectively.

RESULTS

Activated Ras and Src conferred a strong resistance to gefitinib by nearly 30-fold and 200-fold, respectively. Gefitinib induced accumulation of cells in the G0/G1 phase of the cell cycle at 24-h, with progressive expansion of apoptotic cell population in parental HAG-1 cells, but these effects were completely abolished in v-src- or c-H-ras-transfected cell line. Upon gefitinib treatment, EGFR activation and subsequent downstream activation through Erk and Akt were significantly inhibited in HAG-1 cells. By contrast, gefinitib failed to inhibit the activation of both Akt and Erk in v-src-transfected cells and Erk, but not Akt in c-H-ras-transfected cells, despite the blockade of EGFR activation in these respective cell lines. Treatment of v-src-transfected cells with herbimycin A, a Src tyrosine kinase inhibitor, partially reversed the gefitinib resistance, with concomitant inhibition of Akt and Erk.

CONCLUSION

Our results suggest that activated Ras and Src could induce gefitinib resistance by activating either or both of Akt and Erk signaling pathways, thus providing a strategic rationale for assessment of these specific signaling molecules downstream of EGFR to customize treatment.

Src tyrosine kinase augments taxotere-induced apoptosis through enhanced expression and phosphorylation of Bcl-2

Activation of Src, which has an intrinsic protein tyrosine kinase activity, has been demonstrated in many human tumours, such as colorectal and breast cancers, and is closely associated with the pathogenesis and metastatic potential of these cancers. In this study, we have examined the effect of activated Src on the sensitivity to taxotere, an anticancer drug targeting microtubules, using v-src-transfected HAG-1 human gall bladder epithelial cells. As compared with parental HAG-1 cell line, v-src-transfected HAG/src3-1 cells became 5.9 and 7.0-fold sensitive to taxotere for 2 and 24-h exposure, respectively. By contrast, HAG-1 cells transfected with activated Ras, which acts downstream of Src, acquired approximately 2.5- approximately 4.8-fold taxotere resistance. The taxotere sensitivity in HAG/src3-1 cells was reversed, if not completely, by herbimycin A, a specific inhibitor of Src family protein tyrosine kinase, indicating that Src protein tyrosine kinase augments sensitivity to taxotere. Treatment of HAG/src3-1 cells with taxotere resulted in phosphorylation of Bcl-2 and subsequent induction of apoptotic cell death, whereas neither Bcl-2 phosphorylation nor apoptosis occurred in parental or c-H-ras-transfected HAG-1 cells. Interestingly, the Bcl-2 protein is overexpressed in v-src-transfected cell line, compared to those in parental or Ras-transfected cell line. Treatment of HAG/src3-1 cells with herbimycin A significantly reduced the expression and phosphorylation of Bcl-2, and abrogated taxotere-induced apoptosis, suggesting a potential role for Src protein tyrosine kinase in the taxotere-induced apoptotic events. H-7, a protein kinase C inhibitor and wortmannin, a phosphatidylinositol-3 kinase (PI-3 kinase) inhibitor, neither altered taxotere sensitivity nor inhibited taxotere-induced apoptosis in these cells. These data indicate that the ability of activated Src to increase taxotere sensitivity would be mediated by apoptotic events occurring through Src to downstream signal transduction pathways toward Bcl-2 phosphorylation, but not by activated Ras, PI-3 kinase or protein kinase C.

Suppression of malignant growth potentials of v-Src-transformed human gallbladder epithelial cells by adenovirus-mediated dominant negative H-Ras

Although Src transformation of NIH3T3 mouse fibroblasts has been shown to be dependent on Ras function, the signaling mechanism whereby Src induces malignant transformation of human epithelial cells still remains unclear. In the present study, we analyzed the functional role of Ras, which acts downstream of Src in intracellular signaling, in the acquisition of fully neoplastic potentials by v-Src-transformed human gallbladder epithelial cells (HAG/src3-1) by infecting these cells with replication-defective adenovirus vector expressing dominant negative H-Ras (AdCARasY57). High efficiency of gene transduction was demonstrated with the adenovirus vector containing beta-gal gene insert (AdCALacZ). On infection with AdCARasY57, the activity of mitogen-activated protein (MAP) kinase, a major downstream event triggered by Ras, was markedly inhibited over 7 days, indicating that the inhibition of Ras function by AdCARasY57 remains active during this period. AdCARasY57 did not inhibit the monolayer growth of HAG-1 cells transfected with activated H-ras, but inhibited the HAG/src3-1 cells by 30%, as compared with cells infected with AdCALacZ as a control. This growth inhibition by AdCARasY57 was strengthened nearly twofold on surfaces coated with an antiadhesive polymer (poly 2-hydroxyethylmethacrylate) that can quantitate anchorage-independent growth, and was much more pronounced up to 95% when assayed in soft agar. The HAG/src3-1 cells transfected with beta-gal gene produced tumors in nude mice within 4 weeks after implantation, whereas cells infected with AdCARasY57 failed to form tumors during this period. These findings show that Ras function is essential for v-Src-induced anchorage-independent growth in vitro as well as tumorigenesis in vivo, and that mitogenic activity driven by v-Src is not solely dependent on MAP kinase pathway. Because anchorage-independent growth correlates with tumor growth in vivo as well as metastatic potential, targeting Ras would be potentially useful for the treatment of human tumors with elevated Src tyrosine kinase activity.

v-src induces cisplatin resistance by increasing the repair of cisplatin-DNA interstrand cross-links in human gallbladder adenocarcinoma cells

Activation of Src, which has an intrinsic protein tyrosine kinase (PTK) activity, has been demonstrated in human solid tumors, such as colorectal and breast cancers. To investigate the role of activated Src in drug resistance, we evaluated the effect of v-src on the resistance to various anti-cancer drugs using v-src-transfected HAG-1 human gallbladder adenocarcinoma cells. Compared with parental or mock-transfected HAG-1 cells, v-src-transfected HAG/src3-1 cells showed a 3.5-fold resistance to cis-diamminedichloroplatinum (II) (CDDP) but not to doxorubicin, etoposide or 5-fluorouracil. By contrast, activated H-ras, which acts downstream of src, failed to induce resistance to either of these drugs. Furthermore, wortmannin, a phosphatidylinositol (PI) 3-kinase inhibitor, and H7, a protein kinase C (PKC) inhibitor, did not alter CDDP resistance. Evaluation of the kinetics of the removal of DNA interstrand cross-links (ICLs), measured by alkaline elution, showed a significant increase in this removal in HAG/src3-1 cells as compared with mock-transfected cells, though no differences were found in the formation of DNA ICLs between these cell lines. CDDP resistance in v-src-transfected cells was reversed, if not completely, by either herbimycin A or radicicol, specific inhibitors of Src-family PTKs, suggesting that Src tyrosine kinase activity induces CDDP resistance. Moreover, significant reduction in the repair of CDDP-induced DNA ICLs was observed upon treatment with radicicol. The intracellular glutathione content and mRNA expression of topoisomerase II and metallothionein were virtually identical between these cell lines, except for topoisomerase I mRNA. Our data strongly suggest that the ability of activated src, but not ras, to induce CDDP resistance is mediated by augmentation of DNA repair through Src to downstream signal-transduction pathways distinct from either the Ras, PI 3-kinase or PKC pathway.

Interferon-alpha and -gamma inhibit the growth and neoplastic potential of v-src-transformed human epithelial cells by reducing Src tyrosine kinase activity

To investigate whether interferons (IFNs) selectively suppress the growth of solid tumor cells with elevated protein tyrosine kinase (PTK) activity, we evaluated the effect of recombinant IFN-alpha2a and IFN-gamma on the proliferative and neoplastic potentials triggered by p60v-src using v-src-transformed HAG-1 human epithelial cells. When compared with control cells harboring the pSV2neo gene, the monolayer growth of v-src-transformed cell lines was inhibited by both recombinant IFNs, in a dose-dependent manner, whereas growth of ras-transfected cell lines was not affected. Moreover, IFNs markedly reduced the clonogenic growth of v-src-transformed cells in soft-agar rather than monolayer growth, suggesting the preferential activity of IFNs on anchorage-independent growth. Pretreatment of cells with Src or the Src-like PTK inhibitor herbimycin A or radicicol, alleviated dose-dependently the growth-inhibitory activity of IFN-alpha2a against v-src-transformed cells, suggesting that IFNs may share a common inhibitory pathway with Src PTK inhibitors. Accordingly, like herbimycin A, IFNs were found to reduce tyrosine phosphorylation of p60v-src and suppressed in vitro p60v-src kinase activity in v-src-transformed cells. Our data, together with the fact that IFNs inhibit the growth potential driven by Src but not by activated Ras, suggest that inhibition of signal transduction pathway through Src to downstream transduction events may be a primary mechanism of IFN-induced anti-prolifeative and anti-tumoral activity.

Constitutive activation of Jak-2 and Tyk-2 in a v-Src-transformed human gallbladder adenocarcinoma cell line

It is well known that v-Src phosphorylates various substrates on tyrosine residue and associates with tyrosine-phosphorylated proteins as well as proline-rich ligands through its SH2 and SH3 domains, respectively, thereby inducing oncogenic transformation. A signal pathway from the cell surface to genes in the nucleus, the Jak/STAT (signal transducers and activators of transcription) pathway, has been shown to be involved in the signal transduction mechanism mediated by many cytokines and growth factors. Although a member of the STAT family, STAT3 has been reported to be constitutively activated in several v-Src-transformed cells, and it still remains unknown whether Jak molecules, which act upstream of STATs, are involved in the v-Src-induced activation mechanism of STAT3. In this study, we analyzed activations of both Jak and STAT molecules using v-Src-transformed HAG-1 cells derived from a human gallbladder adenocarcinoma. STAT3 was found to be constitutively activated in v-Src-transformed HAG-1 cells, but not in either non-transformed mock-transfected or activated c-H-ras-transfected HAG-1 cells, even though the other known STAT molecules are expressed. Furthermore, both Jak-2 and Tyk-2 were constitutively activated only in v-Src-transformed HAG-1 cells. Association of v-Src with either STAT3 or the Jak molecules was not observed. No change of this activation was detected by either interferon (IFN)-alpha2a or IFN-gamma, which had shown inhibitory effects on the growth of v-Src-transformed HAG-1 cells. These results raise the possibility that Jak-2 and Tyk-2 are both activated by v-Src, thereby contributing to the constitutive activation of STAT3 in the v-Src-transformed cells.

Inhibitors of anchorage-independent growth affect the growth of transformed cells on poly(2-hydroxyethyl methacrylate)-coated surfaces

We have described a microplate colorimetric assay to quantitate anchorage-independent cell growth, using plates coated with an anti-adhesive polymer poly (2-hydroxyethyl methacrylate) (polyHEMA).We investigated whether this method could be applied to human cancer cells of epithelial origin. HAG-1, a non-tumorigenic human gall-bladder carcinoma cell line, and its pSVneo and c-H-ras transfectants, which are also non-tumorigenic, did not grow on a polyHEMA-surface. In contrast, the v-src transformant which produced tumors in nude mice and formed colonies in soft agar, was able to proliferate on the coated surface, suggesting that tumorigenicity of human cancer cells correlates with the ability to grow on a polyHEMA-coated surface. We report on the feasibility of this method as a screening system for inhibitors of oncogenic transformation. Herbimycin A and radicicol, which have been reported to block Src function, suppressed the growth of v-src-transformed NRK and HAG-1 cells on the non-adhesive polyHEMA-surface at concentrations significantly lower than on plastic. Differences in the inhibitory concentrations were not observed with KB cells, and cytotoxic agents such as adriamycin did not show any selectivity between the 2 surfaces. Growth of ras-transformed cells on the coated surface was selectively blocked by L-739,749, a farnesyltransferase inhibitor. The results demonstrate that compounds causing reversion of transformed cells to normal, hence, selectively inhibiting cell growth in anchorage-independent conditions, can be screened using this microtiter plate assay.