Upregulation of xCT by KSHV-encoded microRNAs facilitates KSHV dissemination and persistence in an environment of oxidative stress.
Upregulation of xCT, the inducible subunit of a membrane-bound amino acid transporter, replenishes intracellular glutathione stores to maintain cell viability in an environment of oxidative stress. xCT also serves as a fusion-entry receptor for the Kaposi's sarcoma-associated herpesvirus (KSHV), the causative agent of Kaposi's sarcoma (KS). Ongoing KSHV replication and infection of new cell targets is important for KS progression, but whether xCT regulation within the tumor microenvironment plays a role in KS pathogenesis has not been determined. Using gene transfer and whole virus infection experiments, we found that KSHV-encoded microRNAs (KSHV miRNAs) upregulate xCT expression by macrophages and endothelial cells, largely through miR-K12-11 suppression of BACH-1-a negative regulator of transcription recognizing antioxidant response elements within gene promoters. Correlative functional studies reveal that upregulation of xCT by KSHV miRNAs increases cell permissiveness for KSHV infection and protects infected cells from death induced by reactive nitrogen species (RNS). Interestingly, KSHV miRNAs simultaneously upregulate macrophage secretion of RNS, and biochemical inhibition of RNS secretion by macrophages significantly reduces their permissiveness for KSHV infection. The clinical relevance of these findings is supported by our demonstration of increased xCT expression within more advanced human KS tumors containing a larger number of KSHV-infected cells. Collectively, these data support a role for KSHV itself in promoting de novo KSHV infection and the survival of KSHV-infected, RNS-secreting cells in the tumor microenvironment through the induction of xCT.
Qin
Zhiqiang
Z
Department of Medicine, Hollings Cancer Center, Medical University of South Carolina, Charleston, South Carolina, United States of America.
Freitas
Eduardo
E
Sullivan
Roger
R
Mohan
Sarumathi
S
Bacelieri
Rocky
R
Branch
Drake
D
Romano
Margaret
M
Kearney
Patricia
P
Oates
Jim
J
Plaisance
Karlie
K
Renne
Rolf
R
Kaleeba
Johnan
J
Parsons
Chris
C
D027182:Amino Acid Transport System y+ / Q000096:biosynthesis*; D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism; D002460:Cell Line; D042783:Endothelial Cells / Q000378:metabolism / Q000821:virology; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation / Q000502:physiology*; D019288:Herpesvirus 8, Human / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008264:Macrophages / Q000378:metabolism / Q000821:virology; D051379:Mice; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D009367:Neoplasm Staging; D018384:Oxidative Stress / Q000502:physiology*; D016133:Polymerase Chain Reaction; D026361:Reactive Nitrogen Species / Q000378:metabolism; D012514:Sarcoma, Kaposi / Q000378:metabolism / Q000473:pathology / Q000821:virology*; D014162:Transfection; D015854:Up-Regulation
D027182:Amino Acid Transport System y+; C486316:Bach1 protein, mouse; D050976:Basic-Leucine Zipper Transcription Factors; D035683:MicroRNAs; D026361:Reactive Nitrogen Species; C492255:Slc7a11 protein, mouse