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

Abstract

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.

Active IKKβ promotes the stability of GLI1 oncogene in diffuse large B-cell lymphoma

“…15,16,43 Here, we provide evidence for the presence of noncanonical GLI1 transcriptional activation mediated by IKKb. Using in vitro stromal systems and in vivo models of DLBCL, we found that inhibiting IKKb-mediated NF-kB activation and GLI1 synergistically decreased DLBCL cell viability, supporting a novel therapeutic approach for DLBCL based on concomitant inhibition of NF-kB and GLI1.…”

“…12,14, 16 Here, we demonstrate that IKKb binds GLI1 as part of a multiprotein complex and directly phosphorylates it, promoting stabilization of its intracellular levels. Such stabilization of GLI1 is known to promote the malignant phenotype in multiple cancers, and elevated GLI1 protein accelerates tumor induction in transgenic mice.…”

“…41 One of these transcription factors is GLI1, which is constitutively active in several cancers. 8,10,13,16 We previously showed that GLI1 is constitutively activated in a large subset of DLBCL tumors and that GLI1 contributes to cell proliferation and survival of this lymphoma subtype.…”

“…15,16 Herein, we report that IKKb regulates the degradation and transcriptional activation of GLI1. This is of potential clinical interest because NF-kB signaling is frequently activated by mutations and/or via extracellular signals from the lymphoma microenvironment and plays a key role in DLBCL biology.…”

“…We further demonstrated that the canonical Hh ligand-PTCH1-SMO-GLI1 axis plays important roles in cell proliferation, survival, and chemotolerance in this lymphoma subtype. [12][13][14][15][16] Regulators of GLI1's activities include SNF5, a core subunit of the adenosine trisphophate (ATP)-dependent SWItch/Sucrose NonFermentable chromatin remodeling complex, which modulates its transcriptional activities. 17 Hh signaling, meanwhile, promotes the transcriptional activity of both GLI1 and GLI2 proteins by promoting their deacetylation via HDAC1 upregulation.…”