Enhanced expression of GTP-binding proteins in differentiated U937 monocytic cells: Possible involvement of tyrosine kinase and protein kinase C

Nawab Ali, Devendra K. Agrawal

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Monocytic U937 cells were differentiated into mature macrophages in the presence of 100 nM phorbol 12-myristate 13-acetate (PMA) for 24 h at 37°C. We investigated the alterations in the expression of GTP-binding proteins that take place during differentiation of these cells. A 40 KDa α-subunit of the inhibitory G-protein was identified by specific antibodies to Giα-1/2 and Giα-3 on Western blots and also by ADP-ribosylation catalyzed by pertussis toxin. The expression of the 40 KDa G subunit was increased 3.4 fold in differentiated cells. The expression of a 43 kDa G subunit identified by Western blotting using specific antibody to G and by ADP-ribosylation in the presence of cholera toxin was increased approximately 2 fold in differentiated cells. A faintly recognizable 46 KDa G subunit was also increased but to a lesser extent (1.3 fold). Small molecular weight GTP-binding proteins identified by [35S]GTPγS binding on nitrocellulose blots were also increased significantly. The PMA-induced expression of Giα-1/2 and G subunits was blocked to control level by both genistein and staurosporine, inhibitors of protein tyrosine kinase and protein kinase C, respectively. However, staurosporine was unable to block the PMA-induced expression of Giα-3; this was blocked only by genistein. These data suggest a role for tyrosine kinase and protein kinase C in the expression of G-proteins during differentiation of U937 cells.

Original languageEnglish
Pages (from-to)113-120
Number of pages8
JournalMolecular and Cellular Biochemistry
Issue number2
Publication statusPublished - Nov 1995


All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Genetics
  • Clinical Biochemistry
  • Cell Biology

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