FIG. 5.

Phosphorylation of Ser 261 is not required for Gem-mediated inhibition of Ca²⁺-dependent GH secretion in PC12 cells, whereas mutation of serine 89 results in loss of Gem activity. Secretion of GH was stimulated by addition of high [K⁺] to PC12 cells cotransfected with human GH and empty vector or Gem cDNA. Secreted GH was detected in the supernatant by Western blotting using anti-hGH polyclonal antibody. Total GH and Gem expression were determined by Western analysis of cell lysates. Results shown are representative of at least nine independent experiments.