Cell cycle and apoptosis regulatory protein (CARP)-1 is a novel, adriamycin-inducible, diffuse large B-cell lymphoma (DLBL) growth suppressor

Abstract

Diffuse large B-cell lymphoma (DLCL) accounts for 30-40% of adult non-Hodgkin's Lymphoma (NHL). Current anti-NHL therapies often target cellular growth suppression pathways and include R-CHOP (cyclophosphamide, adriamycin, vincristine, and prednisone plus monoclonal anti-CD20 antibody rituximab). However, since many patients relapse, resistant cells to these therapies remain a significant problem and necessitate development of new intervention strategies. Cell cycle and apoptosis regulatory protein (CARP)-1 functions in a biphasic manner to regulate growth factor as well as chemotherapy (adriamycin, etoposide, or iressa)-dependent signaling. To determine whether CARP-1 is a novel suppressor of lymphoma growth. Flow cytometric analyses coupled with Western immunoblotting, cell growth, apoptosis, and immunocytochemistry methodologies were utilized to determine CARP-1-dependent lymphoma growth inhibition in vitro and in vivo. CARP-1 expression correlated with activated caspase-3 and inversely correlated with activated Akt in DLCL. Exposure to adriamycin stimulated CARP-1 expression and inhibited growth of Raji cells, but not CHOP-resistant WSU-DLCL2 cells. Expression of wild-type CARP-1 or its apoptosis-inducing mutants inhibited growth of Raji as well as CHOP-resistant WSU-DLCL2 cells, in part by activating caspase-9 and apoptosis. Since CARP-1 harbors multiple, apoptosis-promoting subdomains, we investigated whether epigenetic compensation of CARP-1 function by intracellular delivery of trans-activator of transcription (TAT) domain-tagged CARP-1 peptide(s) will inhibit lymphoma growth. Treatments with TAT-tagged CARP-1 peptides suppressed growth of the Raji and WSU-DLCL2 cells by stimulating apoptosis. TAT-CARP-1 (1-198) as well as (896-1150) peptides also suppressed growth of WSU-DLCL2 cell-derived tumor xenografts in SCID mice, while administration of TAT-CARP-1 (1-198) also inhibited growth of WSU-FSCCL cell-derived ascites and prolonged host survival. CARP-1 is a suppressor of NHL growth and could be exploited for targeting the resistant DLCL.