Rhythmic expression of DEC2 protein in vitro and in vivo

Abstract

Basic helix-loop-helix (bHLH) transcription factor DEC2 (bHLHE41/Sharp1) is one of the clock genes that show a circadian rhythm in various tissues. DEC2 regulates differentiation, sleep length, tumor cell invasion and apoptosis. Although studies have been conducted on the rhythmic expression of DEC2 mRNA in various tissues, the precise molecular mechanism of DEC2 expression is poorly understood. In the present study, we examined whether DEC2 protein had a rhythmic expression. Western blot analysis for DEC2 protein revealed a rhythmic expression in mouse liver, lung and muscle and in MCF-7 and U2OS cells. In addition, AMP-activated protein kinase (AMPK) activity (phosphorylation of AMPK) in mouse embryonic fibroblasts (MEFs) exhibited a rhythmic expression under the condition of medium change or glucose-depleted medium. However, the rhythmic expression of DEC2 in MEF gradually decreased in time under these conditions. The medium change affected the levels of DEC2 protein and phosphorylation of AMPK. In addition, the levels of DEC2 protein showed a rhythmic expression and in MCF-7 and U2OS cells. The results showed that the phosphorylation of AMPK immunoreactivity was strongly detected in the liver and lung of knockout mice compared with that of wild-type mice. These results may provide new insights into rhythmic expression and the regulation between DEC2 protein and AMPK activity.

Potential Role of DEC1 in Cervical Cancer Cells Involving Overexpression and Apoptosis

“…DEC2 is more strongly expressed in thyroid cancer cells and carcinoma cells of osteosarcoma than in non-cancerous cells, but weakly expressed in gastric and pancreatic cancer cells [ 4 , 9 , 10 , 11 ]. We showed that DEC2 has circadian expression in tumor cells, such as in mouse sarcoma and in human hepatocellular carcinoma, osteosarcoma and breast cancer cells [ 12 , 13 , 14 ]. We have also shown that DEC1 and DEC2 play important roles in the regulation of apoptosis in human breast and oral cancer [ 1 , 15 , 16 , 17 ].…”

Potential Roles of Dec and Bmal1 Genes in Interconnecting Circadian Clock and Energy Metabolism

“…By using rat-1 fibroblasts, Hirota et al demonstrated that glucose down-regulates the transcription of the Per1 and Per2 genes [ 98 ]. We and others have also reported that in cultured cells, Dec1 expression is increased by glucose supplementation, while glucose depletion decreases both DEC1 and DEC2 protein levels [ 43 , 99 ]. These findings are consistent with in vivo studies that fasting decreases and re-feeding increases Dec1 expression in the murine liver [ 68 , 69 , 70 ].…”

“…First, Dec1 knockout mice decreased lipid levels and oxidative stresses, increasing fibroblast growth factor 21 (FGF21) levels [ 42 ]. Second, we revealed dominant energy sensor phosphorylation AMP-activated protein kinase (pAMPK), which mention at later Section 6 , is markedly increased in Dec2 knockout mice livers [ 43 ]. These evidences suggest that Dec play important roles in the regulation of circadian rhythm and metabolism.…”

“…While the regulation of the molecular clock is modulated by AMPK, the molecular clock in turn regulates AMPK activity [ 43 , 97 ]. We have recently reported that DEC1 directly binds to the E-box box of the Lkb1 promoter and suppresses the expression of the LKB1 protein, thereby reducing the phosphorylation of AMPK [ 97 ].…”

“…We have recently reported that DEC1 directly binds to the E-box box of the Lkb1 promoter and suppresses the expression of the LKB1 protein, thereby reducing the phosphorylation of AMPK [ 97 ]. We also reported that the phosphorylation of AMPK is increased in the liver and lung in Dec2 knockout mice, indicating that DEC2 may also suppress AMPK activity [ 43 ], although the precise mechanism remains to be elucidated. Of note, phosphorylation of AMPK is rhythmic and is inversely correlated with the rhythmic expression of DECs [ 20 , 96 , 97 ], further indicating that AMPK is a downstream target of DECs.…”