p27Kip1-deficient mice exhibit accelerated growth hormone-releasing hormone (GHRH)-induced somatotrope proliferation and adenoma formation

Abstract

p27 Kip1 (p27) controls cell cycle progression by binding to and inhibiting the activity of cyclin dependent kinases. Disruption of the p27 gene in mice (p277/7) results in increased body growth with a disproportionate enlargement of the spleen, thymus, testis, ovary and pituitary. The increase in pituitary size is due to selective hyperplasia of the intermediate lobe (IL) while the anterior lobe (AL) is not overtly a ected. p27 heterozygous mice (p27+/7), as well as p277/7 mice, are hypersensitive to radiation-and chemical-induced tumors compared to wildtype (p27+/+) littermates. Therefore, unlike classical tumor suppressors, only a reduction in p27 levels is necessary to predispose tissues to secondary tumor promoters. Consistent with these studies is the fact that the p27 gene sequence and mRNA levels appear normal in human pituitary adenomas while p27 protein levels are decreased. Therefore, a reduction in p27 levels could be su cient to sensitize pituitary cells to tumorigenic factors. To test this hypothesis, metallothionein promoter-driven, human growth hormone-releasing hormone (MT-hGHRH) transgenic mice, that exhibit somatotrope hyperplasia before 9 months of age and subsequent adenoma formation with 30 ± 40% penetrance, were crossbred with p27+/7 mice for two successive generations to produce p27+/+, p27+/7 and p277/7 mice that expressed the hGHRH transgene. At 10 ± 12 weeks of age, p277/7 and p27+/+, hGHRH mice were larger than their p27+/+ littermates and displayed characteristic hyperplasia of the IL and AL, respectively. Expression of the hGHRH transgene in both p27+/7 and p277/7 mice selectively expanded the population of somatotropes within the AL, where pituitaries of p27+/7, hGHRH and p277/7, hGHRH mice were two-and ®vefold larger than p27+/+, hGHRH pituitaries, respectively. There was also a synergistic e ect of hGHRH transgene expression and p27-de®ciency on liver, spleen and ovarian growth. At 6 ± 8 months of age, 83% of p27+/7, hGHRH mice displayed macroscopic AL adenomas (4100 mg), while all pituitaries from p27+/+, hGHRH mice remained hyperplastic (520 mg). In contrast to the dramatic e ects of p27-de®ciency on hGHRH-induced organ growth, elimination of p53, by crossbreeding MT-hGHRH mice to p53-de®cient mice, did not augment the hyperplastic/ tumorigenic e ects of hGHRH transgene expression.Taken together these results demonstrate that a reduction in p27 expression is su cient to sensitize somatotropes to the proliferative actions of excess GHRH, resulting in the earlier appearance and increased penetrance of hGHRH-induced pituitary tumors.

Genetic mosaics reveal both cell-autonomous and cell-nonautonomous function of murine p27 Kip1

“…Ink4c double knockouts demonstrate increased pars distalis proliferation in response to growth hormone-releasing hormone administration, and ovary transplants suggest that female infertility in p27 Kip1 -deficient mice is due to a combination of ovarian and pituitary defects (19,20). Our p27loxP and p27stop mouse models in combination with other cell-type-specific Cre transgenes may be useful to determine whether other pituitary cells contribute to these phenotypes.…”

Cdk4 Is Indispensable for Postnatal Proliferation of the Anterior Pituitary

“…Slides were rinsed in phosphate-buffered saline, pH7.4, containing 0.01% Triton X-100 or boiled 10 min in 10 mM pH 6.0 sodium citrate for Ki67 staining. The sections were then treated for 30 min with 1.5% normal goat serum and incubated for 2 h with monkey anti-GH antibody (14) at a dilution of 1:100,000 or with mouse anti-Ki67 antibody (Vector Laboratories, Burlingame, CA) at 1:1,000. Slides were then rinsed in phosphate-buffered saline/Triton and incubated for 30 min with biotinylated secondary antibody (Vector Laboratories) at a dilution of 1:200, rinsed in phosphate-buffered saline, and incubated in avidin-peroxidase conjugate (Elite Vectastain; Vector Laboratories).…”

An essential role of p27 downregulation in fenvalerate-induced cell growth in human uterine leiomyoma and smooth muscle cells

“…In support of this, stabilization of p27 has been proposed to be clinically beneficial for various tumors by counterregulating proliferation and promoting undifferentiated cells to redifferentiate (26). Similarly in vivo, genetically engineered mice deficient in p27 were determined to have increased susceptibility to cancers after exposure to chemicals or irradiation risk factors (13,28). Thereafter, this concept brings a new question to mind: how does Fen regulate p27?…”