Tumor escape in a Wnt1-dependent mouse breast cancer model is enabled by p19Arf/p53 pathway lesions but not p16Ink4a loss

• Published in: The Journal of clinical investigation 2008-01, Vol.118 (1), p.51-63
• Main Authors: Debies, Michael T., Gestl, Shelley A., Mathers, Jessica L., Mikse, Oliver R., Leonard, Travis L., Moody, Susan E., Chodosh, Lewis A., Cardiff, Robert D., Gunther, Edward J.
• Format: Article
• Language: English
• ISSN: 0021-9738
• DOI: 10.1172/JCI33320

Breast cancers frequently progress or relapse during targeted therapy, but the molecular mechanisms that enable escape remain poorly understood. We elucidated genetic determinants underlying tumor escape in a transgenic mouse model of Wnt pathway–driven breast cancer, wherein targeted therapy is simulated by abrogating doxycycline-dependent Wnt1 transgene expression within established tumors. In mice with intact tumor suppressor pathways, tumors typically circumvented doxycycline withdrawal by reactivating Wnt signaling, either via aberrant (doxycycline-independent) Wnt1 transgene expression or via acquired somatic mutations in the gene encoding β-catenin. Germline introduction of mutant tumor suppressor alleles into the model altered the timing and mode of tumor escape. Relapses occurring in the context of null Ink4a/Arf alleles (disrupting both the p16 Ink4a and p19 Arf tumor suppressors) arose quickly and rarely reactivated the Wnt pathway. In addition, Ink4a/Arf -deficient relapses resembled p53 -deficient relapses in that both displayed morphologic and molecular hallmarks of an epithelial-to-mesenchymal transition (EMT). Notably, Ink4a/Arf deficiency promoted relapse in the absence of gross genomic instability. Moreover, Ink4a/Arf -encoded proteins differed in their capacity to suppress oncogene independence. Isolated p19 Arf deficiency mirrored p53 deficiency in that both promoted rapid, EMT-associated mammary tumor escape, whereas isolated p16 Ink4a deficiency failed to accelerate relapse. Thus, p19 Arf /p53 pathway lesions may promote mammary cancer relapse even when inhibition of a targeted oncogenic signaling pathway remains in force.