Utilization of a novel dissimilarity approach to identify a novel mechanism of merkel cell polyomavirus small tumor antigen nuclear import responsible for the development of merkel cell carcinoma

Stetson University, Inc. received a $547,875 Project Grant award from the National Cancer Institute (NCI) under the Cancer Biology Research program (CFDA 93.396), effective September 22, 2025, with a completion date of August 31, 2028. The award supports fundamental research investigating the mechanisms of Merkel cell polyomavirus (MCPYV) small tumor antigen nuclear import to identify novel pathways responsible for Merkel cell carcinoma (MCC) development. This three-year research project employs an innovative dissimilarity approach by comparing MCPYV with non-oncogenic human polyomaviruses to identify unique molecular mechanisms that distinguish MCPYV as the only oncogenic human polyomavirus, with the goal of developing more effective therapeutic interventions for MCC, a rare but aggressive skin cancer with significantly higher mortality rates than melanoma.

The research directly contributes to the NCI's Cancer Biology Research program objectives by providing fundamental information on cancer etiology and mechanisms through investigation of tumor antigen function and nuclear localization pathways. By understanding the distinctive mechanisms by which MCPYV drives tumorigenesis—specifically the unique capability of MCPYV small tumor antigen to achieve nuclear localization without a conventional nuclear localization signal—the project aims to identify therapeutic vulnerabilities and advance methods for prevention, detection, diagnosis, and treatment of MCC in the approximately 80% of cases associated with MCPYV infection.

Abstract

Merkel cell carcinoma (MCC) is a rare but aggressive skin cancer with a mortality rate three times higher than melanoma. Treatment for MCC remains a challenge, with only approximately 50% of individuals responding to current therapies. Notably, 80% of MCC cases are caused by merkel cell polyomavirus (mcpyv); understand- ING the mechanisms of mcpyv tumorigenesis is thus of critical importance for the development of effective therapies for MCC. In mcpyv-positive MCC, the small (ST) and large (LT) tumor antigens are responsible for the development of MCC. Mcpyv belongs to a family of 15 human polyomaviruses (hpyv), all of which encode their own ST and LT; however, only mcpyv is associated with cancer. Seeing the lack of other oncogenic hpyvs for comparison as a limitation, earlier research has focused on the similarities between mcpyv and two oncogenic, non-human polyomaviruses (simian virus 40 [SV40] and murine polyomavirus [mupyv]). How- ever, this approach has been limited by mcpyv, SV40, and mupyv each utilizing a different tumor antigen as their dominant transforming protein: ST is the dominant transforming protein of mcpyv but is only an acces- sory player in SV40- and mupyv- mediated transformation. Instead, this project uses an innovative "dissimi- larity approach" to exploit the fact that mcpyv is uniquely tumorigenic among hpyvs. By identifying the DIF- ferences between mcpyv and two skin-tropic, non-oncogenic hpyvs, trichodysplasia spinulosa polyomavirus (tspyv) and human polyomavirus 7 (HPYV7), one could identify the unique mechanisms responsible for mcpyv oncogenesis. Using this approach, IT was found that mcpyv ST is uniquely capable of nuclear localiza- tion despite the absence of a nuclear localization signal (NLS) and that nuclear localization was necessary for cellular transformation. To further investigate mcpyv ST nuclear localization and its role in the unique trans- formative capabilities of mcpyv ST, the following aims are proposed. The first aim seeks to identify the mcpyv ST novel NLS (nvnls) by focusing on a region of 30 amino acids (MST30) responsible for nuclear localization. The second aim will determine whether the nvnls is responsible for the unique transforming abilities of mcpyv ST among hpyvs and will facilitate understanding of the hpyv determinants in inducing malignant or non-malignant disease. The third aim seeks to further understand the mechanism by which mcpyv ST can AC- complish nuclear import by investigating interactions with nuclear transport proteins such as importin and NU- clear pore complex proteins. Together, the aims investigated in this proposal will further our understanding of cellular nuclear import, determinants of hpyv oncogenesis, and the mechanisms of mcpyv ST-induced MCC, which may collectively prove influential in developing novel, efficacious therapies for MCC. All aspects of these investigations will be performed by stetson university undergraduate students, thereby providing students with invaluable biomedical research experience, and strengthening the research culture of stetson university.