Myosin phosphatase targeting subunit 1 undergoes phosphorylation and translocates from the nucleus to cytoplasm during skeletal muscle differentiation

• Published in: The FASEB journal 2006-03, Vol.20 (4), p.A804-A804
• Main Authors: Xia, Donglan, Stull, James T., Kamm, Kristine E.
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.20.4.A804-a

The myosin phosphatase targeting subunit 1 (MYPT1) for protein Ser/Thr phosphatase type 1, regulates many contractile‐related cellular events by affecting myosin II phosphorylation. MYPT1‐GFP was reported to be in nuclei of NIH3T3 fibroblasts due to an N‐terminal nuclear localization signal; however it was in the cytoplasm with serum starvation (Wu et al, J Muscle Res Cell Motil. 2005). We found endogenous MYPT1 enriched in nuclei in skeletal muscle C2C12 myoblasts but in the cytoplasm of sarcomeric α‐actinin‐positive C2C12 myotubes. Transient transfections with GFP‐tagged MYPT1 displayed the same localizations as endogenous MYPT1 whereas GFP‐tagged, N‐terminal fragments of MYPT1s (residues 1–300 and 1–500) were in the nuclei of both myoblasts and myotubes indicating a loss of targeting regulation. Western blotting indicated that MYPT1 may be phosphorylated at multiple sites during differentiation of C2C12 cells. Phosphorylated MYPT1 at Thr694 or Thr852 was found in both nuclei and cytoplasm suggesting these two sites may not be related to MYPT1′ s cytoplasmic translocation. Inhibition of Rho‐associated kinase (ROCK) by Y27632 had no affect on MYPT1 phosphorylation or myocyte differentiation. Inactivation of the PI‐3K/Akt pathway by LY290042 inhibited cytoplasmic translocation as well as differentiation. Sites of phosphorylation are currently being identified. These studies will address whether MYPT1 phosphorylation by Akt regulates translocation from the nucleus to the cytoplasm during skeletal muscle differentiation (This work supported by NIH).