Hedgehog signaling pathway is activated in diffuse large B-cell lymphoma and contributes to tumor cell survival and proliferation

Hedgehog (HH) signaling is important in the pathogenesis of several malignancies. Recently, we described that HH signaling proteins are commonly expressed in diffuse large B-cell lymphoma (DLBCL); however, the functional role of HH pathway in DLBCL has not been explored. Here, we assessed the possibility that HH pathway activation contributes to the survival of DLBCL. We found that HH signaling inhibition induces predominantly cell-cycle arrest in DLBCL cells of germinal center (GC) B-cell type, and apoptosis in DLBCL cells of activated B-cell (ABC) type. Apoptosis after HH signaling inhibition in DLBCL cells of ABC type was associated with downregulation of BCL2; however HH inhibition was not associated with BCL2 downregulation in DLBCL of GC type. Functional inhibition of BCL2 significantly increased apoptosis induced by HH inhibition in DLBCL cells of both types. We also showed that DLBCL cells synthesize, secrete and respond to endogenous HH ligands, providing support for the existence of an autocrine HH signaling loop. Our findings provide novel evidence that dysregulation of HH pathway is involved in the biology of DLBCL and have significant therapeutic implications as they identify HH signaling as a potential therapeutic target in DLBCL, in particular for those lymphomas expressing the HH receptor smoothened.

Suppressor of cytokine signaling 3 expression in anaplastic large cell lymphoma

Using a cDNA microarray, we found that suppressor of cytokine signaling 3 (SOCS3) is highly expressed in anaplastic lymphoma kinase (ALK)+ anaplastic large cell lymphoma (ALCL) cell lines. As SOCS3 is induced by activated signal transducer and activator of transcription 3 (STAT3), and ALK activates STAT3, we hypothesized that SOCS3 may play a role in ALK+ ALCL pathogenesis via the Janus kinase 3 (JAK3)-STAT3 pathway. Using ALCL cell lines, we show by coimmunoprecipitation experiments that SOCS3 physically binds with JAK3 in vitro, and that JAK3 inhibition by WHI-P154 downregulates SOCS3 expression. Western blot analysis confirmed expression of SOCS3 and also showed coexpression of phosphorylated (activated) STAT3 (pSTAT3). Direct sequencing of the SOCS3 gene showed no mutations or alternative splicing. In ALCL tumors that were assessed by immunohistochemistry, nine of 12 (75%) ALK+ tumors were SOCS3 positive and eight (67%) coexpressed pSTAT3. In comparison, 18 of 25 (72%) ALK-- tumors were SOCS3 positive and seven (28%) coexpressed pSTAT3. These results show that SOCS3 is overexpressed in ALCL, attributable to JAK3-STAT3 activation and likely related to ALK in ALK+ tumors. However, SOCS3 is also expressed in tumors that lack STAT3 and ALK suggesting alternative mechanisms of upregulation.