This dissertation, "Salt-inducible Kinases Function as a Host Restriction to Human T-cell Leukemia Virus Type 1 Transcription" by Weiwei, Gao, 高蔚为, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author.
Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-1 Tax is the major viral transactivator and transforming protein centrally involved in the proviral transcription, transformation and proliferation of infected T-cells as well as progression of diseases caused by HTLV-1 infection. Salt-inducible kinases (SIKs) are serine/threonine protein kinases belonging to the AMPK-related kinase (AMPK-RK) family. SIK subfamily consists of three isoforms named SIK1, SIK2 and SIK3 respectively. We have previously demonstrated the negative regulatory role of SIK1 in Tax-mediated activation of proviral transcription from long terminal repeats (LTR). In this study, we reported that both SIK2 and SIK3 exhibited a kinase-dependent suppressive effect on Tax-activated LTR transcription. We also found that SIK1, SIK2 and SIK3 act additively to suppress Tax activation of LTR. We further demonstrated that the SIK2- and SIK3-mediated suppression on LTR transcription was achieved through phosphorylation of TORC1, an essential transcriptional coactivator of CREB required for Tax-mediated transcriptional activation of LTR. Our findings revealed a new function of SIK2 and SIK3 in host restriction to HTLV-1 transcription. Pharmaceutical activation of SIKs or upstream kinase such as LKB1 may provide a new strategy for anti-HTLV-1 therapy.