J. Biol. Chem., Vol. 265, Issue 14, 7814-7818, 05, 1990
Decreased expression of the type I isozyme of cAMP-dependent protein kinase in tumor cell lines of lung epithelial origin
CA Lange-Carter, T Fossli, T Jahnsen and AM Malkinson
Molecular and Environmental Toxicology Program, School of Pharmacy, University of Colorado, Boulder 80309.
A spontaneous transformant derived from a mouse lung epithelial cell line
exhibited decreased cAMP-dependent protein kinase (PKA) activity. DEAE
column chromatography demonstrated that this was caused by specific loss of
the type I PKA isozyme (PKA I). Western immunoblot analysis indicated that
indeed several mouse lung tumor-derived cell lines and spontaneous
transformants of immortalized, nontumorigenic lung cell lines contained
less PKA I regulatory subunit (RI) protein than normal cell lines. PKA II
regulatory subunit protein differed only slightly among cell lines and
showed no conspicuous trend between normal and neoplastic cells. The
decrease in RI was apparently concomitant with decreased catalytic (C)
subunit levels in neoplastic cells since no free catalytic subunit activity
was detected by DEAE chromatography. Northern blot analysis using RI alpha
and C alpha cDNA probes showed that the levels of RI alpha and C alpha
mRNAs paralleled their intracellular protein concentrations; neoplastic
cell lines contained significantly less RI alpha and C alpha mRNAs than the
normal cell line. The decreased expression of both RI and C subunits
therefore results in a net decrease of PKA I in neoplastic lung cells, an
isozymic difference which may account for the differential effects of cAMP
analogs on cell growth and differentiation in normal and neoplastic cells.