Merkel Cell Polyomavirus Small T Antigen Mediates Microtubule Destabilization To Promote Cell Motility and Migration

Abstract

Merkel cell carcinoma (MCC) is an aggressive skin cancer of neuroendocrine origin with a high propensity for recurrence and metastasis. Merkel cell polyomavirus (MCPyV) causes the majority of MCC cases due to the expression of the MCPyV small and large tumor antigens (ST and LT, respectively). Although a number of molecular mechanisms have been attributed to MCPyV tumor antigen-mediated cellular transformation or replication, to date, no studies have investigated any potential link between MCPyV T antigen expression and the highly metastatic nature of MCC. Here we use a quantitative proteomic approach to show that MCPyV ST promotes differential expression of cellular proteins implicated in microtubule-associated cytoskeletal organization and dynamics. Intriguingly, we demonstrate that MCPyV ST expression promotes microtubule destabilization, leading to a motile and migratory phenotype. We further highlight the essential role of the microtubule-associated protein stathmin in MCPyV ST-mediated microtubule destabilization and cell motility and implicate the cellular phosphatase catalytic subunit protein phosphatase 4C (PP4C) in the regulation of this process. These findings suggest a possible molecular mechanism for the highly metastatic phenotype associated with MCC.IMPORTANCE Merkel cell polyomavirus (MCPyV) causes the majority of cases of Merkel cell carcinoma (MCC), an aggressive skin cancer with a high metastatic potential. However, the molecular mechanisms leading to virally induced cancer development have yet to be fully elucidated. In particular, no studies have investigated any potential link between the virus and the highly metastatic nature of MCC. We demonstrate that the MCPyV small tumor antigen (ST) promotes the destabilization of the host cell microtubule network, which leads to a more motile and migratory cell phenotype. We further show that MCPyV ST induces this process by regulating the phosphorylation status of the cellular microtubule-associated protein stathmin by its known association with the cellular phosphatase catalytic subunit PP4C. These findings highlight stathmin as a possible biomarker of MCC and as a target for novel antitumoral therapies.

Restricted Protein Phosphatase 2A Targeting by Merkel Cell Polyomavirus Small T Antigen

“…MCV sT binding to PP4C has also been found to promote cell motility through microtubule destabilization, and this may contribute to the aggressiveness of MCV-MCC tumors (53). Our MS and immunoprecipitation analyses confirm the binding of MCV sT and PP4C.…”

Epidemiology, biology and therapy of Merkel cell carcinoma: conclusions from the EU project IMMOMEC

“…a sT can (i) preserve 4E-BP1 hyperphosphorylation resulting in dysregulated cap-dependent translation [31], (ii) through inhibition of SCF Fbx7 ubiquitin ligase stabilize their cellular targets and MCPyV LT [32], (iii) interact with NEMO thereby inhibiting NF-κB-mediated transcription [33–35], (iv) lead to a motile and migratory phenotype by promoting microtubule destabilization [36], (v) elevate aerobic glycolysis by regulating MCT-1 levels [37] and (vi) inactivate p53 pathway through recruitment of MAX and MYCL and binding to P400 complex resulting in increased expression of the p53 inhibitor MDM2. b In tumor cells, the C-terminal domains of LT containing several crucial elements required for viral replication are consistently truncated by tumor-associated mutations.…”

The Oncogenic Small Tumor Antigen of Merkel Cell Polyomavirus Is an Iron-Sulfur Cluster Protein That Enhances Viral DNA Replication

“…This sT activity results in a global stimulation of cap-dependent translation (12). In addition, binding of MCPyV sT to PP4C has been implicated in the destabilization of microtubules and increased cell motility, possibly contributing to the metastatic nature of MCC (17).…”