Constitutive high Bcl2 and BclxL levels impair autophagic Hodgkin Lymphoma cell death.

FRANCO CORTES, CLAUDIA ALEJANDRA; OLIVER MARTOS, FRANCISCO JAVIER; RANUNCOLO, STELLA MARIS

Mar del Plata

Congreso; LXI Reunión Científica Anual de la Sociedad Argentina de Investigación Clínica (SAIC), LXIV Reunión Anual de la Sociedad Argentina de Inmunología (SAI), XLVIII Reunión Anual de la Sociedad Argentina de Farmacología Experimental (SAFE).; 2016

Sociedad Argentina de Investigación Clínica (SAIC), Sociedad Argentina de Inmunología (SAI) y Sociedad Argentina de Farmacología Experimental (SAFE).

Hodgkin lymphoma (HL) is a lymphatic system malignancy derived from germinal center B cells. Despite chemosensitive HL patients can be cured, 40% are refractory to current chemotherapy regimens and relapse within 12 months from diagnosis. Even more, following second or third chemo schemes, 55% of those patients remain unresponsive. This and the young age of diagnosis highlight the need to better understand HL molecular biology.We have previously reported that HL relies on the alternative NFkB pathway, mediated by reB/NIK, to survive. Its constitutive activativation is the result of stable NIK protein expression both in human HL cell lines and patient biopsies. Depletion of either relB or NIK by shRNAs or pharmacological NIK inhibitors induce HL cell death. To further explain the relB depletion induced phenotype in L1236, U-H01 and KM-H2 HL cell lines, we investigated the target genes that might account for the HL cell death. Chromatin immunoprecipitation showed relB/p52 bound to Bcl2 and BclxL promoters, among other cell cycle control genes. We detected a significant downregulation of both Bcl2 and BclxL mRNA and protein levels, following relB or NIK knockdown, indicating relB direct regulation. Interestingly a Bcl2 cDNA, with the shrelB target sequence mutated, was capable of partially rescue the toxicity induced by relB depletion in L1236, U-H01 and KM-H2 HL cells. Furthermore, co-immunoprecipitation assays revealed that Bcl2 and BclxL interact with the autophagy executing protein Beclin1, inhibiting cell death. Despite the well known Bcl2 and BclxL antiapoptotic activity, dead HL cells, showed autophagic features upon relB depletion. The analysis of the apoptosis activation markers, PARP1 and caspase3, did not change in shRNA relB knockdown HL cells as compared to controls.These results shed light on new targetable signalling pathways that play key roles in HL cell survival. High Bcl2 and BclxL levels, sequester Beclin1, inhibiting autophagic HL cell death.