p57KIP2 expression and loss of heterozygosity during immortal conversion of cultured human mammary epithelial cells
The authors have uncovered a novel role for the cyclin-dependent kinase inhibitor, p57KIP2, during the immortalization of cultured human mammary epithelial cells (HMEC). HMEC immortalized following chemical carcinogen exposure initially expressed little or no telomerase activity, and their telomeres continued to shorten with passage. Cell populations whose mean terminal restriction fragment (TRF) length declined and exhibited slow heterogeneous growth, and contained many non-proliferative cells. These conditionally immortal HMEC cultures accumulated large quantities of p57 protein. With continued passage, the conditionally immortal cell populations very graduall2048nverted to a fully immortal phenotype of good uniform growth, expression of high levels of telomerase activity, and stabilization of telomere length. The fully immortal good growing HMEC did not accumulate p57 in G0 or during the cell cycle. DNA and RNA analysis of mass populations and individual subclones of conditionally immortal HMEC line 184A1 showed that continued growth of conditionally immortal cells with critically short telomeres was repeatedly accompanied by loss of the expressed p57 allele, and transient expression of the previously imprinted allele. Conditionally immortal 184A1 with mean TRF > 3 kb infected with retroviruses containing the p57 gene exhibited premature slow heterogeneous growth. Conversely, exogenous expression of hTERT, the catalytic subunit of telomerase, in 184A1 with mean TRF > 3 kb prevented both the slow heterogeneous growth phase and accumulation of p57 in cycling populations. These data indicate that in HMEC which have overcome replicative senescence, p57 may provide an additional barrier against indefinite proliferation. Overcoming p57 mediated growth inhibition in these cells may be crucial for acquisition of the unlimited growth potential thought to be critical for malignant progression.
- Research Organization:
- Lawrence Berkeley National Lab., CA (United States)
- Sponsoring Organization:
- USDOE Director, Office of Science. Office of Biological and Environmental Research. Life Sciences Division; National Institutes of Health (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5209638
- Report Number(s):
- LBNL-44111; CODEN: CNREA8
- Journal Information:
- Cancer Research, Vol. 59:20; ISSN 0008-5472
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
NEOPLASMS
ENZYME INHIBITORS
PHOSPHOTRANSFERASES
EPITHELIUM
MAMMARY GLANDS
MAN
CARCINOGENS
GENE REGULATION
CELL PROLIFERATION
CARCINOGENESIS
DISEASES
PHOSPHORUS-GROUP TRANSFERASES
ANIMAL TISSUES
GLANDS
PRIMATES
PATHOGENESIS
TRANSFERASES
BODY
ORGANS
MAMMALS
ENZYMES
VERTEBRATES
PROTEINS
ANIMALS
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550900 - Pathology