High levels of truncated RHAMM cooperate with dysfunctional p53 to accelerate the progression of pancreatic cancer

Pancreatic cancer has the lowest survival rate in all types of cancer. Pancreatic cancer patients are often diagnosed at advanced stages. A better therapeutic development for this devastating disease is urgently needed. Receptor for hyaluronan-mediated motility (RHAMM), not expressed in adult pancreas, has been suggested as a prognostic factor and a potential therapeutic target for pancreatic ductal adenocarcinoma (PDAC) and pancreatic neuroendocrine tumor (PNET). In this study, we initially sought to determine whether genetic deletion of RHAMM would slow down pancreatic cancer progression using Rhamm -/- mice. However, we found that Rhamm -/- mice expressed a truncated HMMR Δexon8-16 protein at higher abundance levels than wild-type RHAMM. While HMMR Δexon8-16 did not enable malignant progression of pancreatic intraepithelial neoplasia in p48-Cre ; LSL-KRAS G12D mice, it accelerated the formation of invasive PDAC and shortened the survival of p48-Cre ; LSL-KRAS G12D mice with heterozygous p53 knockout. Kras G12D PDAC mice with homozygous p53 knockout mice died around 10 weeks, and the effect of HMMR Δexon8-16 was not apparent in these mice with short-life span. In addition, HMMR Δexon8-16 shortened the survival of PNET-bearing RIP-Tag mice, which had inactivated p53. In our analysis of TCGA dataset, pancreatic cancer patients with mutant TP53 or loss of one copy of TP53 had higher RHAMM expression, which, combined, predicted worse outcomes. Taken together, by collaborating with dysfunctional p53, high levels of HMMR Δexon8- 16 that lacks the centrosome targeting domain and degrons for interaction with the Anaphase-Promoting Complex (APC) accelerated pancreatic cancer progression.