Invasive human pituitary tumors express a point-mutated alpha-protein kinase-C.

Abstract

Protein kinase-C (PKC) is a ubiquitous eukaryotic kinase that plays a key role in transmembrane signaling and influences important cellular processes, such as proliferation. Increases in its activity and expression have been demonstrated in adenomatous human pituitaries, with protein expression being the highest in invasive tumors (1). Moreover, in these same invasive tumors, the mean increase in expression (8.9-fold) does not correlate with the mean increase in activity (2.6-fold), suggesting a dysfunction in PKC in these tumors. Here, we show that the PKC alpha-isoform (alpha PKC) is overexpressed in human pituitary tumors. The complete sequencing of the PKC cDNA from four invasive tumors has revealed a point mutation that is absent in the noninvasive tumors analyzed. The point mutation is located at position 294 of the protein, in the V3 region, leading to a substitution of a negatively charged aspartic acid by an apolar glycine. Thus, not only is alpha PKC overexpressed in human pituitary tumors, but it is also structurally altered in the invasive subpopulation of these tumors.

Ectopic expression of a mutant form of PKCα originally found in human tumors: aberrant subcellular translocation and effects on growth control

“…32 were selected for analysis. They expressed around 20 times the protein (624 and 619 respectively), which is consistent with the maximum increase in PKCa expression found in pituitary tumors (Alvaro et al, 1992(Alvaro et al, , 1993. Two R6-hPKCa-wt clones were also selected for analysis, no.…”

“…This factor allowed to correct the amount of total protein used in the enzymatic reaction, in order to use an equal amount of enzyme. Values represent the mean of three independent assays, and are considered as the experimental value minus the`bland value' obtained without any activator (Alvaro et al, 1993;Pre vostel et al, 1995). The goal of this work was to characterize the biochemical properties of this enzyme mutant, its phenotypic eects on cells where it has been stably overexpressed, and to assess if it could be implicated in tumorigenesis or tumor progression.…”

“…Speci®cally, a`mutation' 5'-primer ± (871-920) 5'-gaaggtgagtactacaacgtacccattccggaagggggcgaggaaggaaa-3' was designed which would incorporate the point mutation found in pituitary tumors at position 908 (Alvaro et al, 1993). This mutation was created in the oligonucleotide by substitution of an adenosine by a guanine.…”

“…Recently a mutant of PKCa has been discovered in human pituitaries tumors and shown to be present only in a subpopulation of tumors characterized by their invasive phenotype (Alvaro et al, 1993). The mutation is located in the V3 hinge region separating the catalytic from the regulatory domains of the enzyme (at position 294 of the amino acid sequence) and leads to the substitution of an aspartic acid by a glycine.…”

hpttg is over-expressed in pituitary adenomas and other primary epithelial neoplasias

“…G s asubunit gene point mutations result in the constitutive activation of adenyly cyclase and have been identi®ed in about 30% of GH-secreting pituitary adenomas in di erent series of patients (Landis et al, 1989;Lyons et al, 1990). Activating mutations of ras and protein kinase C genes have been reported in rare aggressive tumors (Pei et al, 1994;Alvaro et al, 1993;Karga et al, 1992). Alterations of tumor suppressor genes such as RB or p53 are very infrequent (Cryns et al, 1993;Herman et al, 1993;Sumi et al, 1993), and the rate of men1 gene deletion or mutation seems to be low in sporadic pituitary tumors (Zhuang et al, 1997).…”