Both normal and transforming PCPH proteins have guanosine diphosphatase activity but only the oncoprotein cooperates with ras in activating extracellular signal-regulated kinase ERK1
Ja. Recio et al., Both normal and transforming PCPH proteins have guanosine diphosphatase activity but only the oncoprotein cooperates with ras in activating extracellular signal-regulated kinase ERK1, CANCER RES, 60(6), 2000, pp. 1720-1728
Previous reports from our laboratory described the activation of the PCPH g
ene into the PCPH oncogene (mt-PCPH reported previously as Cph) by a single
point mutational deletion, As a consequence, the mt-PCPH oncoprotein is a
truncated form of the normal PCPH protein. Although both proteins have ribo
nucleotide diphosphate-binding activity, only mt-PCPH acted synergistically
with a human H-Ras oncoprotein to transform murine NIH3T3 fibroblasts, We
report here the expression of the PCPH and mt-PCPH proteins in Escherichia
coli and the finding that the purified bacterial recombinant proteins have
intrinsic guanosine diphosphatase (GDPase) activity. However, expression of
the Syrian hamster PCPH and mt-PCPH proteins in haploid yeast strains engi
neered to be GDPase deficient by targeted disruption of the single GDA1 all
ele did not complement their glycosylation-disabled phenotype, suggesting t
he existence of significant functional differences between the mammalian an
d yeast enzymes. Results from transient cotransfections into NIH3T3, COS-7,
or 293T cells indicated that, in mammalian cells, both PCPH and mt-PCPH ca
use an overall down-regulation of the stimulatory effect of epidermal growt
h factor or the activated ms or raf oncogenes on the Ras/mitogen-activated
protein kinase/extracellular signal-regulated kinase (ERK) signaling pathwa
y. However, despite this overall negative regulatory role on Ras signaling,
mt-PCPH, but not PCPH, cooperated with the Ras oncoprotein to produce a pr
olonged stimulation of the phosphorylation of ERK1 but had no effect on the
phosphorylation levels of ERK2, These results represent a clear difference
between the mechanisms of action of PCPH and mt-PCPH and suggest that the
ability to cause a sustained activation of ERK1 may be an important determi
nant of the transforming activity of mt-PCPH.