THE EFFECT OF PHOSPHORYLATION OF MOUSE SAMHD1 ON RESTRICTION OF HIV-1 AND MURINE LEUKEMIA VIRUS INFECTIONS
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Series/Report no.:2015 Edward F. Hayes Graduate Research Forum. 29th
Background: The dNTPase SAMHD1 functions as an HIV-1 restriction factor in non-dividing cells by limiting intracellular dNTP levels required to complete viral reverse transcription. Phosphorylation of human SAMHD1 (hSAMHD1) at residue threonine (T) 592 by cyclin dependent kinase 1 (CDK1) and CDK2 impairs its restriction of HIV-1 infection. Mouse SAMHD1 (mSAMHD1) shares 72-74% protein sequence identity with hSAMHD1, and also restricts HIV-1 infection in non-dividing cells. However, it is unknown whether phosphorylation of mSAMHD1 regulates its restriction of retroviral infection. Results: We identified and confirmed that T634 is a phosphosite of mSAMHD1 in dividing cells by mass spectrometry and using a phospho-specific antibody. Using specific inhibitors of CDK1 and CDK2 decreased the level of T634 phosphorylated mSAMHD1 in dividing cells. We generated human U937 and mouse NIH3T3 cell lines stably expressing mSAMHD1 wild-type (WT), phospho-ablative (T634A) or phospho-mimetic (T634D) mutants to examine the effect of T634 phosphorylation on mSAMHD1-mediated restriction of HIV-1 or murine leukemia virus (MLV), respectively. In differentiated U937 cells, overexpression of mSAMHD1 WT or the mutants significantly restricted HIV-1 infection and reduced the intracellular dNTP levels. In dividing NIH3T3 cells, mSAMHD1 WT or the mutants modestly reduced MLV infection. Conclusions: CDK1 and CDK2 phosphorylate T634 of mSAMHD1 in dividing cells. Restriction of HIV-1 infection in non-dividing cells and MLV infection in dividing cells by mSAMHD1 is independent of its T634 phosphorylation. Our results suggest different mechanisms of regulating retroviral restriction by hSAMHD1 and mSAMHD1.
Professional Biological Sciences: 2nd Place (The Ohio State University Edward F. Hayes Graduate Research Forum)
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