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Modulation of the c-Met/hepatocyte growth factor pathway in small cell lung cancer
Gautam Maulik1, Takashi Kijima, Patrick C Ma
1Department of Adult Oncology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA.
Abstract:
The c-Met receptor tyrosine kinase and its ligand HGF (hepatocyte growth factor) have been shown to be involved in angiogenesis, cellular motility, growth, invasion, and differentiation. The role of c-Met/HGF axis in small cell lung cancer (SCLC) has not been reported previously. We have determined the expression of p170(c-Met) precursor and p140(c-Met) beta-chain in seven SCLC cell lines by immunoblotting. We used the SCLC cell line H69, which expressed an abundant amount of c-Met to study the function and downstream effects of c-Met activation. Stimulation of H69 cells with HGF (40 ng/ml, 6-h stimulation) significantly altered cell motility of the SCLC cells with increased formation of filopodia and membrane ruffling, characterized as membrane blebbing, as well as increased migration of the cellular clusters were seen. We have further studied the signal transduction pathways of HGF/c-Met in the H69 cell line. The stimulation of H69 with HGF (40 ng/ml, >24 h, maximal at 1 h) increased the amount of reactive oxygen species formed by 34%. HGF stimulation (40 ng/ml, 7.5-min stimulation) of H69 cells showed increased tyrosine phosphorylated bands identified at M(r) 68,000, 120,000-140,000, and 200,000. Some of these tyrosine-phosphorylated bands were identified as the focal adhesion proteins paxillin, FAK, PYK2, and the c-Met receptor itself. Phospho-specific antibodies show that tyrosines at amino acid (a.a.) 31 of paxillin, and autophosphorylation sites at a.a. 397 of p125FAK, and a.a. 402 of PYK2 are phosphorylated in response to HGF/c-Met signaling. We also demonstrate that the Hsp90 inhibitor geldanamycin, which also affects c-Met, reduced the growth and viability of four of four SCLC cell lines by 25% to 85%, over a 72-h time period. Geldanamycin caused apoptosis of SCLC cells, as well as led to increased levels of Hsp70 but not Hsp90. These results demonstrate that c-Met/HGF pathway is functional in SCLC, and it would be useful to target this pathway toward novel therapy.
Insights
The c-Met/HGF pathway is active in small cell lung cancer (SCLC), influencing cell motility and growth. Inhibiting this pathway with geldanamycin shows promise for novel SCLC therapies.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- The c-Met receptor tyrosine kinase and its ligand, hepatocyte growth factor (HGF), regulate key cellular processes.
- The involvement of the c-Met/HGF axis in small cell lung cancer (SCLC) remains largely unexplored.
Purpose of the Study:
- To investigate the expression and functional role of the c-Met/HGF pathway in SCLC.
- To explore potential therapeutic strategies targeting the c-Met pathway in SCLC.
Main Methods:
- Immunoblotting to determine c-Met expression in SCLC cell lines.
- Stimulation of SCLC cells with HGF to assess effects on cell motility and signal transduction.
- Analysis of downstream signaling molecules, including focal adhesion proteins and reactive oxygen species.
- Treatment with Hsp90 inhibitor geldanamycin to evaluate its impact on SCLC cell growth, viability, and apoptosis.
Main Results:
- c-Met precursor (p170) and beta-chain (p140) were detected in SCLC cell lines.
- HGF stimulation enhanced SCLC cell motility, filopodia formation, membrane ruffling, and migration.
- HGF/c-Met signaling increased reactive oxygen species production and tyrosine phosphorylation of focal adhesion proteins (paxillin, FAK, PYK2).
- Geldanamycin significantly reduced SCLC cell growth and viability, inducing apoptosis and increasing Hsp70 levels.
Conclusions:
- The c-Met/HGF pathway is functionally active in SCLC.
- Targeting the c-Met/HGF pathway, potentially through Hsp90 inhibition, represents a promising therapeutic strategy for SCLC.