The HGF/c-Met Signaling Pathway in Hodgkin Lymphoma.

Hodgkin lymphoma (HL) is a B-cell neoplasm characterized by a minority of neoplastic cells, the so-called Hodgkin and Reed-Sternberg (HRS) cells, which are located within an extensive infiltrate of reactive cells. Aberrant signaling of various receptor tyrosine kinases (RTKs) via autocrine or paracrine mechanisms contributes to the survival and proliferation of HRS cells. Activation of the hepatocyte growth factor (HGF)/c-Met signaling pathway has been implicated in the pathophysiology of many cancers, but its role in HL is poorly investigated. In this study, we investigated the expression of c-Met and HGF in HL patient tissues and studied the cell physiological effects of the HGF/c-Met signaling pathway using a c-Met tyrosine kinase inhibitor SU11274 in HL cell lines.

The expression of c-Met and HGF in HL patient tissues was studied by immunohistochemistry on a HL tissue microarray. The c-Met expression level was determined by Western blotting, while HGF mRNA and protein levels were measured by quantitative (q)RT-PCR and ELISA in four HL cell lines, i.e. L428, KMH2, L1236 and U-HO1. The effects of SU11274 treatment on the activity of the HGF/c-Met signaling pathway was determined by detection of phosphorylated downstream targets by Western blotting. Effects on cell growth and cell cycle were determined by 3-(4,5- Dimethylthiazol -2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay and by flow cytometry with Propidium iodide (PI), respectively.

C-Met was detected in HRS cells in 55% (26/47) of HL patient tissues. Expression of HGF was detected in HRS cells in 5 c-Met positive and 2 c-Met negative HL patient tissues. C-Met was highly expressed in L428 compared to three other HL cell lines, whereas HGF was highly expressed in KMH2 and not or only weakly in the other three HL cell lines. Detectable levels of phosphorylated c-Met (p-Met) were observed only in L428 consistent with the high basal expression level of c-Met. Phosphorylation of c-Met, Akt and Erk1/2 were upregulated upon HGF stimulation of L428 cells. This activation could be blocked by inhibiting c-Met activation with SU11274. In functional studies, SU11274 suppressed cell growth in L428, promoted G2/M cell cycle arrest after 24h incubation, and induced tetraploidy after 48h. Washing of the cells after induction of G2/M arrest resulted in normal cell cycle progression indicating that the G2/M cell cycle arrest was reversible. Inhibition of PI3K, MEK1/2 and Erk1/2, three downstream targets of the HGF/c-Met signaling pathway, also induced G2/M cell cycle arrest in L428, indicating that these factors are involved in the G2/M cell cycle arrest induced by SU11274.

Co-expression of c-Met and HGF in HRS cells was observed in 11% of the HL patient tissues and HGF/c-Met signaling pathway regulates cell growth and cell cycle progression in L428 cells.

No relevant conflicts of interest to declare.