Two pathways of p27^Kip1degradation are required for murine lymphoma driven by Myc and EBV latent membrane protein 2A

Abstract

27Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A), expressed in EBV 28 latency, contributes to Burkitt Lymphoma (BL) development in a murine model by acting as a 29 constitutively active B cell receptor (BCR) mimic. Mice expressing both LMP2A and MYC 30 transgenes (LMP2A/-MYC) develop tumors significantly faster than mice only expressing MYC 31 (-MYC). Previously, we demonstrated the cell cycle inhibitor p27 Kip1 is present at significantly 32 lower levels in LMP2A/-MYC mice due to increased post-translational degradation. P27 Kip1 33 degradation can occur in the cytoplasm following phosphorylation on serine 10 (S10), or in the 34 nucleus via the SCF Skp2 complex, which depends on Cks1. We previously demonstrated a S10A 35 knock-in of p27 Kip1 (p27 S10A/S10A ), which prevented S10 phosphorylation, failed to significantly 36 delay tumor onset in LMP2A/-MYC mice. We also previously demonstrated that a Cks1 37 knockout partially delayed tumor onset in LMP2A/-MYC mice, but onset was still significantly 38 faster than in -MYC mice. Here, we have combined both genetic manipulations in what we call 39 p27 Super mice. LMP2A/-MYC/p27 Super mice and -MYC/p27 Super mice both displayed dramatic 40 delays in tumor onset. Strikingly, tumor development in LMP2A/-MYC/p27 Super mice was later 41 than in -MYC mice and not significantly different from -MYC/p27 Super mice. The p27 Super 42 genotype also normalized G 1 -S phase cell cycle progression, spleen size, and splenic 43 architecture in LMP2A/-MYC mice. Our results reveal both major pathways of p27 Kip1 44 degradation are required for the accelerated BL development driven by LMP2A in our BL model 45 and that blocking both degradation pathways is sufficient to delay Myc-driven tumor 46 development with or without LMP2A.47 48 Importance 49 Burkitt lymphoma (BL) is a cancer that primarily affects children. The side effects of 50 chemotherapy highlight the need for better BL treatments. Many BL tumors contain Epstein-Barr 51 virus (EBV) and our goal is to determine what makes EBV-positive BL different from EBV-52 negative BL. This may lead to more specific treatments for both types. All cases of BL require 53 overexpression of MYC. Mice engineered to express an EBV LMP2A along with MYC 54 (LMP2A/-MYC mice) develop tumors much more quickly than mice only expressing MYC (-55 MYC mice). Blocking degradation of the cell cycle inhibitor protein p27 Kip1 in LMP2A/-MYC 56 mice causes tumors to develop later than in -MYC mice, showing that p27 Kip1 degradation may 57 play a larger role in EBV-positive BL than EBV-negative. Furthermore, our studies suggest the 58 cell cycle may be an attractive target as a treatment option for LMP2A positive cancers in 59 humans. 60 61 Introduction 62 Epstein-Barr virus (EBV) is a -herpesvirus that establishes latent infection in over 95% 63 of the world's population by adulthood(1). EBV latency occurs primarily in B cells and has been 64 associated with several B cell cancers, including Burkitt Lymphoma (BL)(2). There are thr...