Non-circadian aspects of BHLHE40 cellular function in cancer
Zsofia Kiss1,2, Maria Mudryj1,4 and Paramita M. Ghosh1,2,3
1 VA Northern California Health Care System, Sacramento, CA, USA
2 Department of Urology, University of California Davis School of Medicine, Sacramento, CA, USA
3 Department of Biochemistry and Molecular Medicine, University of California Davis School of Medicine, Sacramento, CA, USA
4 Department of Microbiology and Immunology, University of California, Davis, Davis, CA, USA
Correspondence:
Paramita M. Ghosh, email:
Keywords: BHLHE40/DEC1/STRA13/SHARP2, E-box, PI3K/Akt/mTOR, AMPK, HIF-1α
Received: November 11, 2019 Accepted: February 27, 2020 Published: March 22, 2020
Abstract
While many genes specifically act as oncogenes or tumor suppressors, others are tumor promoters or suppressors in a context-dependent manner. Here we will review the basic-helix-loop-helix (BHLH) protein BHLHE40, (also known as BHLHB2, STRA13, DEC1, or SHARP2) which is overexpressed in gastric, breast, and brain tumors; and downregulated in colorectal, esophageal, pancreatic and lung cancer. As a transcription factor, BHLHE40 is expressed in the nucleus, where it binds to target gene promoters containing the E-box hexanucleotide sequence, but can also be expressed in the cytoplasm, where it stabilizes cyclin E, preventing cyclin E-mediated DNA replication and cell cycle progression. In different organs BHLHE40 regulates different targets; hence may have different impacts on tumorigenesis. BHLHE40 promotes PI3K/Akt/mTOR activation in breast cancer, activating tumor progression, but suppresses STAT1 expression in clear cell carcinoma, triggering tumor suppression. Target specificity likely depends on cooperation with other transcription factors. BHLHE40 is activated in lung and esophageal carcinoma by the tumor suppressor p53 inducing senescence and suppressing tumor growth, but is also activated under hypoxic conditions by HIF-1α in gastric cancer and hepatocellular carcinomas, stimulating tumor progression. Thus, BHLHE40 is a multi-functional protein that mediates the promotion or suppression of cancer in a context dependent manner.
