Forskolin inhibits protein kinase c-induced mitogen activated protein kinase activity in mc3t3-e1 osteoblasts

Suresh R. Siddhanti, J. Edward Hartle, Leigh Quarles

Research output: Contribution to journalArticle

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Abstract

We recently demonstrated that stimulation of DNA synthesis in MC3T3-E1 osteoblasts involves cross-talk between protein kinase C (PKC)-dependent pathways and activation of possible nonreceptor tyrosine kinases. In the current investigation we examined whether the Raf-1/MAP kinase kinase (MKK)/mitogen-activated protein kinase (MAPK) cascade integrates cross-talk between G protein-coupled second messengers and protein tyrosine phosphorylation in osteoblasts. We investigated the effects on DNA synthesis, protein tyrosine phosphorylation, and Raf-1, MKK, and MAPK activities of PKC activation by phorbol 12-myristate 13-acetate (PMA) and of cAMP elevation by forskolin (FSK) in MC3T3-E1 osteoblasts. We found that PMA-stimulated DNA synthesis was associated with increments in tyrosine phosphorylation of p44mapk (ERK1) and p42mapk (ERK2) and activation of Raf-1, MKK, and MAPK in these cells. FSK treatment of osteoblasts, which raised intracellular cAMP levels and inhibited DNA synthesis, blocked PKC-stimulated tyrosine phosphorylation of p44mapk (ERK1) and p42mapk (ERK2) as well as inhibited PKC-stimulated MAPK and Raf-1 activities. Despite this, PMA activated the intermediate MKK step of the Raf-1/MKK/MAPK cascade in the presence of FSK. The differential inhibition of PMA-stimulated Raf-1 and MKK activities by FSK suggests that PKC activates both Raf-1-dependent and -independent pathways in MC3T3-E1 osteoblasts. Moreover, the noncoordinate effects of FSK on PMA-stimulated MKK and MAPK activities indicates the presence of a additional distal cAMP-dependent inhibitory mechanisms.

Original languageEnglish (US)
Pages (from-to)4834-4841
Number of pages8
JournalEndocrinology
Volume136
Issue number11
DOIs
StatePublished - Jan 1 1995
Externally publishedYes

Fingerprint

Proto-Oncogene Proteins c-raf
Mitogen-Activated Protein Kinase Kinases
Colforsin
Mitogen-Activated Protein Kinases
Osteoblasts
MAP Kinase Kinase Kinases
Protein Kinases
Protein Kinase C
Acetates
Tyrosine
Phosphorylation
DNA
Second Messenger Systems
GTP-Binding Proteins
Protein-Tyrosine Kinases
Proteins
phorbol-12-myristate

All Science Journal Classification (ASJC) codes

  • Endocrinology

Cite this

Forskolin inhibits protein kinase c-induced mitogen activated protein kinase activity in mc3t3-e1 osteoblasts. / Siddhanti, Suresh R.; Hartle, J. Edward; Quarles, Leigh.

In: Endocrinology, Vol. 136, No. 11, 01.01.1995, p. 4834-4841.

Research output: Contribution to journalArticle

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