Date Published: January 17, 2017
Publisher: Public Library of Science
Author(s): Pınar Aksoy, Patricio I. Meneses, Lawrence Banks.
Persistent infection with high-risk human papillomavirus (HPV) genotype is a major factor leading to many human cancers. Mechanisms of HPV entry into host cells and genome trafficking towards the nucleus are incompletely understood. Dopachrome tautomerase (DCT) was identified as a cellular gene required for HPV infection in HeLa cells on a siRNA screen study. Here, we confirm that DCT knockdown significantly decreases HPV infection in the human keratinocyte HaCaT cells as was observed in HeLas. We investigated the effects of DCT knockdown and found that DCT depletion caused increased reactive oxygen species (ROS) levels, DNA damage and altered cell cycle in HaCaT cells. We observed increased viral DNA localization at the endoplasmic reticulum but an overall decrease in infection in DCT knockdown cells. This observation suggests that viral DNA might be retained in the ER due to altered cell cycle, and viral particles are incapable of further movement towards the nucleus in DCT knockdown cells.
Human papillomavirus (HPV) is a non-enveloped small DNA virus. The capsid consists of two virally encoded proteins, L1 and L2 [1, 2]. The L1 protein has been shown to mediate the initial host cell binding at the extracellular matrix or at the plasma membrane [3–5] via the capsid’s interaction with heparan sulfate proteoglycans (HSPGs) [6–8]. After the initial binding event, several conformational changes of the capsid by cellular proteases allow for viral internalization [9–14]. After the virus is internalized into the host cells, the L2 protein, and perhaps L1, accompanies the viral DNA through its journey to the nucleus [15–18]. The viral genome traffics through the endolysosomal sytem, Golgi complex, and the ER before localizing into nucleus during mitosis for viral DNA replication [19–25]. Although we have identified some of the key players in HPV infection, we still lack a complete understanding of this process. Recent genome-wide screening studies provided us with invaluable insights that can help us reveal new players in HPV biology [24, 25].
DCT is an enzyme mainly involved in melanin synthesis in melanosomes. The expression of melanosomes is restricted to melanocytes and retinal pigment epithelial (RPE) cells . Besides its main role in melanin synthesis, DCT is also involved in 1) detoxification of the melanin precursors; 2) it is known to limit DNA damage caused by chemotherapeutic agents, X-ray or UVB and gamma irradiation in melanoma cells, and 3) it decreases cell’s sensitivity to oxidative stress by increasing cellular glutathione (GSH) levels [28, 36, 46–49]. In addition to these functions, a recent genome-wide siRNA screen in HeLa cells surprisingly indicated a role for DCT in HPV16 infection . However, the details of how DCT is involved in HPV infection have not been investigated yet.