Project C02

Principal Investigator

Prof. Dr. Nicole Fischer & Prof. Dr. Arwen Pearson

Medical Center Hamburg-Eppendorf 
& Universität Hamburg

C2

PhD candidate

Tommaso Mari

C2

Project Summary

Characterization of the structural and molecular mechanism how Merkel cell polyomavirus (MCPyV) Large T-Antigen tumor hallmark mutations occur 

The human tumor virus Merkel cell polyomavirus (MCPyV) establishes persistent infections in ~80% of the healthy human population and is the leading cause of Merkel cell carcinoma (MCC), a rare skin cancer in immunosuppressed and elderly individuals [1-3]. MCPyV causally contributes to MCC through (i) monoclonal integration of viral DNA into the host genome and (ii) expression of the constitutive viral oncoproteins LTtrunc and sT in tumor cells. Although the virus is highly prevalent, few carriers will develop MCC during their lifetime. Two independent events must occur to initiate tumorigenesis: viral integration and the occurrence of tumor-specific mutations resulting in a highly expressed truncated LT protein (LTtrunc) [4]. Previous studies, including our work, have shown that mutations within the early region resulting in LTtrunc are located downstream of the retinoblastoma protein (Rb) binding domain and upstream or within the viral origin binding domain of LT, suggesting positive selection for the N-terminus of LT and/or negative selection against the C-terminus of LT [5].

Furthermore, we and others have shown that integrated MCPyV in the host genome often occurs as concatamers with all viral genomes carrying the same mutations in the LT gene [5,6,7]. Interestingly, it was previously shown for SV40 that replication fork stalling can occur and impairment of the host DNA repair mechanism can result in viral DNA intermediates [8]. Based on these previous findings for SV40 and knowledge of the MCPyV DNA integration pattern, we hypothesize that the hallmark mutations of the MCPyV LT gene identified in MCC occur during the process of viral DNA replication. Possible causes of the mutations could be cell stress-induced stalling of the DNA polymerase complex, DNA sequence-induced stalling, or random errors of the polymerase in the presence of dysfunctional DNA repair mechanisms. Based on these previous observations, this project aims to elucidate the molecular mechanisms that contribute to truncating mutations within the early gene region of MCPyV.

C2

References

  1. Becker JC, Stang A, Hausen AZ, et al. Epidemiology, biology and therapy of Merkel cell carcinoma: conclusions from the EU project IMMOMEC. Cancer Immunol Immunother. 2018 Mar;67(3):341-351. doi: 10.1007/s00262-017-2099-3.
  2. Feng H, Shuda M, Chang Y, et al. Clonal integration of a polyomavirus in human Merkel cell carcinoma. Science. 2008 Feb 22;319(5866):1096-100. doi: 10.1126/science.1152586. 
  3. Grundhoff A, Fischer N. Merkel cell polyomavirus, a highly prevalent virus with tumorigenic potential. Curr Opin Virol. 2015 Oct;14:129-37. doi: 10.1016/j.coviro.2015.08.010. 
  4. Borchert S, Czech-Sioli M, Neumann F, et al. High-affinity Rb binding, p53 inhibition, subcellular localization, and transformation by wild-type or tumor-derived shortened Merkel cell polyomavirus large T antigens. J Virol. 2014 Mar;88(6):3144-60. doi: 10.1128/JVI.02916-13. 
  5. Czech-Sioli M, Günther T, Therre M, et al. High-resolution analysis of Merkel Cell Polyomavirus in Merkel Cell Carcinoma reveals distinct integration patterns and suggests NHEJ and MMBIR as underlying mechanisms. PLoS Pathog. 2020 Aug 24;16(8):e1008562. doi: 10.1371/journal.ppat.1008562.
  6. Starrett GJ, Thakuria M, Chen T, et al. Clinical and molecular characterization of virus-positive and virus-negative Merkel cell carcinoma. Genome Med. 2020 Mar 18;12(1):30. doi: 10.1186/s13073-020-00727-4. 
  7. Schrama D, Sarosi EM, Adam C, et al Characterization of six Merkel cell polyomavirus-positive Merkel cell carcinoma cell lines: Integration pattern suggest that large T antigen truncating events occur before or during integration. Int J Cancer. 2019 Aug 15;145(4):1020-1032. doi: 10.1002/ijc.32280. 
  8. Sowd GA, Li NY, Fanning E. ATM and ATR activities maintain replication fork integrity during SV40 chromatin replication. PLoS Pathog. 2013;9(4):e1003283. doi: 10.1371/journal.ppat.1003283.