Expression of p27^Kip1 and c-Jun activation binding protein 1 are inversely correlated in systemic anaplastic large cell lymphoma

Purpose: p27^KiP1(p27) is a universal cyclin-dependent kinase inhibitor that inhibits cell cycle transition from G₁ to S phase and is primarily regulated at the post-transcriptional level via the ubiquitin-proteasome pathway. In vitro data suggest that p27 degradation may be accelerated by the c-Jun activation domain binding protein-1 (JAB1), originally identified as a coactivator of the gene regulatory AP-1 proteins. We assessed p27 and JAB1 in systemic anaplastic large cell lymphoma (ALCL), a group of tumors in which a substantial subset overexpresses anaplastic lymphoma kinase (ALK). Experimental Design: The study included 5 ALK-positive ALCL cell lines, namely Karpas 299, JB-6, SR-786, SU-DHL1, and TG-S1, and 66 ALCL tumors (24 ALK positive and 42 ALK negative). The cell lines were analyzed by Western blot methods, and the tumors were assessed immunohistochemically. Results: SU-DHL1 and TG-S1 cells were positive for p27 and negative for JAB1, whereas SR-786 and JB-6 cells were positive for JAB-1 but negative for p27. Karpas 299 expressed p27 at relatively low levels and JAB1 at high levels. Using a 10% cutoff, p27 was positive in 12 of 66 (18.2%) ALCL tumors (5 ALK positive and 7 ALK negative), whereas JAB1 was detected in 47 of 53 (88.7%) tumors (15 ALK positive and 32 ALK negative) assessed. p27 and JAB1 expression were inversely correlated (Spearman r = -0.27, P = 0.03). For 54 ALCL patients with complete follow-up, and in separate analyses of patients with ALK-positive or -negative tumors, p27 expression correlated with poorer prognosis. Conclusions: p27 is absent or expressed at low levels in most ALCL tumors and inversely correlates with JAB1. These findings suggest that JAB1-mediated degradation of p27, allowing cell cycle progression, may play a role in the pathogenesis of ALCL.