Gene expression levels of Casein kinase 1 (CK1) isoforms are correlated to adiponectin levels in adipose tissue and site-specific phosphorylation mediated by CK1 influences multimerization of adiponectin

Introduction:

Adiponectin, an adipocytokine with anti-inflammatory, antidiabetic, anti-atherogenic, and anti-cancer features, is mainly secreted by adipose tissue. Human adiponectin has an N-terminal collagenous domain and a C-terminal globular domain and builds characteristic homomeres including trimers, hexamers and high molecular weight (HMW) 12 – 18-mers. The beneficial effects of adiponectin in humans are primarily mediated by its HMW isoform. Posttranslational modifications play an important role in regulating activity and complex formation of adiponectin. Phosphorylation is considered to be another most common posttranslational modification that may alter the activity, life span, or cellular localization of proteins.

Aim:

Since members of the CK1 family are involved in the regulation of various signaling pathways. we ask here whether they are able to modulate the functions of adiponectin.

Materials and methods:

Gene expression levels and their correlations in adipose tissue from morbid obese (MO) patients were analyzed by immunohistochemistry, RT-PCR and Immunoprecipitation. Next, adiponectin is phosphorylated in vitro was identified from kinase assays, phosphopeptide analysis and phosphoamino acid analysis. Site-specific phosphorylation influence on complex formation of adiponectin was investigated by Western blot analysis in cellular lysates of omental adipose tissue or serum with or without protein phosphatase 1 treatment and in cellular lysates of SGBS adipocytes cells treated with CK1 inhibitor IC261.

Results:

CK1δ is expressed in adipose tissue and that the expression of CK1 δ correlates with adiponectin. Furthermore, adiponectin coimmunoprecipitates with CK1δ and is phosphorylated by CK1δ at serine 174 and threonine 235, thereby influencing the formation of adiponectin oligomeric complexes. Furthermore, inhibition of CK1δ in human adipocytes by IC261 leads to an increase in basal and insulin-stimulated glucose uptake.

Conclusion:

Site-specific phosphorylation of adiponectin, especially at sites targeted by CK1δ in vitro, provides an additional regulatory mechanism for modulating adiponectin complex formation and function.