Two pathways of p27Kip1degradation are required for murine lymphoma driven by Myc and EBV latent membrane protein 2A

Abstract

AbstractEpstein-Barr virus (EBV) latent membrane protein 2A (LMP2A), expressed in EBV latency, contributes to Burkitt Lymphoma (BL) development in a murine model by acting as a constitutively active B cell receptor (BCR) mimic. Mice expressing both LMP2A andMYCtransgenes (LMP2A/λ-MYC) develop tumors significantly faster than mice only expressingMYC(λ-MYC). Previously, we demonstrated the cell cycle inhibitor p27Kip1is present at significantly lower levels in LMP2A/λ-MYCmice due to increased post-translational degradation. P27Kip1degradation can occur in the cytoplasm following phosphorylation on serine 10 (S10), or in the nucleus via the SCFSkp2complex, which depends on Cks1. We previously demonstrated a S10A knock-in of p27Kip1(p27S10A/S10A), which prevented S10 phosphorylation, failed to significantly delay tumor onset in LMP2A/λ-MYCmice. We also previously demonstrated that aCks1knockout partially delayed tumor onset in LMP2A/λ-MYCmice, but onset was still significantly faster than in λ-MYCmice. Here, we have combined both genetic manipulations in what we call p27Supermice. LMP2A/λ-MYC/p27Supermice and λ-MYC/p27Supermice both displayed dramatic delays in tumor onset. Strikingly, tumor development in LMP2A/λ-MYC/p27Supermice was later than in λ-MYCmice and not significantly different from λ-MYC/p27Supermice. The p27Supergenotype also normalized G1-S phase cell cycle progression, spleen size, and splenic architecture in LMP2A/λ-MYCmice. Our results reveal both major pathways of p27Kip1degradation are required for the accelerated BL development driven by LMP2A in our BL model and that blocking both degradation pathways is sufficient to delay Myc-driven tumor development with or without LMP2A.ImportanceBurkitt lymphoma (BL) is a cancer that primarily affects children. The side effects of chemotherapy highlight the need for better BL treatments. Many BL tumors contain Epstein-Barr virus (EBV) and our goal is to determine what makes EBV-positive BL different from EBV-negative BL. This may lead to more specific treatments for both types. All cases of BL require overexpression ofMYC. Mice engineered to express an EBV LMP2A along withMYC(LMP2A/λ-MYCmice) develop tumors much more quickly than mice only expressing MYC (λ-MYCmice). Blocking degradation of the cell cycle inhibitor protein p27Kip1in LMP2A/λ-MYCmice causes tumors to develop later than in λ-MYCmice, showing that p27Kip1degradation may play a larger role in EBV-positive BL than EBV-negative. Furthermore, our studies suggest the cell cycle may be an attractive target as a treatment option for LMP2A positive cancers in humans.