Evidence that TSC2 acts as a transcription factor and binds to and represses the promoter of Epiregulin

Abstract

The TSC2 gene, mutated in patients with tuberous sclerosis complex (TSC), encodes a 200 kDa protein TSC2 (tuberin). The importance of TSC2 in the regulation of cell growth and proliferation is irrefutable. TSC2 in complex with TSC1 negatively regulates the mTOR complex 1 (mTORC1) via RHEB in the PI3K-AKT-mTOR pathway and in turn regulates cell proliferation. It shows nuclear as well as cytoplasmic localization. However, its nuclear function remains elusive. In order to identify the nuclear function of TSC2, a whole-genome expression profiling of TSC2 overexpressing cells was performed, and the results showed differential regulation of 266 genes. Interestingly, transcription was found to be the most populated functional category. EREG (Epiregulin), a member of the epidermal growth factor family, was found to be the most downregulated gene in the microarray analysis. Previous reports have documented elevated levels of EREG in TSC lesions, making its regulatory aspects intriguing. Using the luciferase reporter, ChIP and EMSA techniques, we show that TSC2 binds to the EREG promoter between −352 bp and −303 bp and negatively regulates its expression. This is the first evidence for the role of TSC2 as a transcription factor and of TSC2 binding to the promoter of any gene.

FAM172A modulates apoptosis and proliferation of colon cancer cells via STAT1 binding to its promoter

“…The EMSA annlysis was condocted as previously described ( 17 ). Probes for EMSA were synthesized by a biotin label at the 3′ end (Invitrogen, Shanghai, China).…”

Mammalian target of rapamycin complex 2 (mTORC2) controls glycolytic gene expression by regulating Histone H3 Lysine 56 acetylation

“…AKT regulates the nuclear/cytoplasmic shuttling of TSC2 [65]. Also, TSC2 localize to the nucleus and acts as a transcription factor by binding to the promoter of epiregulin gene and suppressing the expression [66]. It will be interesting to investigate whether TSC2 localize along with mTORC2 in the nucleus to regulate the levels of H3K56 acetylation.…”

mTOR Signaling and Neural Stem Cells: The Tuberous Sclerosis Complex Model

“…As already reported, there is different evidence revealing mTORC1-independent functions of TSC1/2 [ 73 , 74 , 75 , 76 , 77 ]. This information could be very useful to develop new therapeutic strategies bypassing mTOR signaling pathway avoiding severe adverse events related to mTOR-inhibitor long term treatments.…”

“…Results obtained using mTOR inhibitors further support the existence of a direct association between hyperactivation of mTORC1 and TSC pathology [ 71 , 72 ]. However, evidence revealing mTORC1-independent functions of TSC1/2, such as the role of TSC2 as transcription factor, has been also produced [ 73 , 74 , 75 , 76 , 77 ]. Further investigation in this regard may be helpful to understand those aspects of TSC that are not unequivocally attributable to mTORC1 activity.…”