Down-regulation of SM22/transgelin gene expression during H9c2 cells differentiation
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The embryonic rat ventricle H9c2 cells maintain a proliferative state (P condition) in the presence of 10% FCS. However, by reducing serum concentration and in the presence of retinol acetate, proliferation is stopped, myogenic transdifferentiation is inhibited while cardiac differentiation is preserved (D condition). Two-dimensional gel electrophoresis and mass spectrometry analysis was used to define the modifications of the nuclear proteome occurring during the P-to-D transition. Among the proteins observed as modified, a reduced expression of the SM22/transgelin protein was associated with the D state. Also SM22 mRNA levels were reduced during P-to-D transition. Cell transfection experiments indicated that this decrease was partially due to a reduction of the SM22 promoter activity. GATA-4 had a repressive effect on SM22 promoter activity. Thus, since GATA-4 is known as a target of retinoids and may act as a transcriptional repressor, a mechanism to explain the SM22 reduction during the P-to-D transition is tentatively proposed. Immunohistochemical studies on heart cells confirmed the nuclear localization of SM22. Moreover, a differential expression of this protein in different districts of the human heart embryo was detected. Therefore, these data suggest that SM22 expression is regulated during heart development.
KeywordsTransgelin Cardiomyocyte Differentiation GATA-4
Matrix assisted laser desorption ionization-time of flight
Micro-liquid chromatography-electrospray-ion trap-tandem mass spectrometry
This work is funded by grants from MIUR to GD (PRIN No. 2007N8P32H_002), GT (FIRB No. RBRN07BMCT—Italian Human ProteomeNet) and AS (MERIT) and from CNR (AG.P04.015 and RSTL 862). Expression vector GATA-4 was provided by Prof. D. Salvatore (University Federico II, Naples).
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