ErbB2/Neu-induced, cyclin D1-dependent transformation is accelerated in p27-haploinsufficient mammary epithelial cells but impaired in p27-null cells.
ErbB2/Neu destabilizes the cyclin-dependent kinase (Cdk) inhibitor p27 and increases expression of cyclin D1. Therefore, we studied the roles of p27 and cyclin D1 in ErbB2-mediated mammary epithelial cell transformation. Overexpression of ErbB2 or cyclin D1 in p27(+/-) primary murine mammary epithelial cells resulted in increased proliferation, cyclin D1 nuclear localization, and colony formation in soft agar compared to those in p27(+/+) cells. In contrast, ErbB2- or cyclin D1-overexpressing p27(-/-) cells displayed reduced proliferation, anchorage-independent growth, Cdk4 activity, cyclin D1 expression, and cyclin D1 nuclear localization compared to wild-type cells. A cyclin D1 mutation in its nuclear export sequence (T286A) partially rescued nuclear localization of cyclin D1 in p27(-/-) cells but did not increase proliferation or Cdk4 kinase activity. Overexpression of E2F1, however, increased proliferation to the same degree in p27(+/+), p27(+/-), and p27(-/-) cells. Mammary glands from MMTV (mouse mammary tumor virus)-neu/p27(+/-) mice exhibited alveolar hyperplasia, enhanced proliferation, decreased apoptosis, and accelerated tumor formation compared to MMTV-neu/p27(+/+) glands. However, MMTV-neu/p27(-/-) glands showed decreased proliferation, cyclin D1 expression, and Cdk4 activity, as well as markedly prolonged tumor latency, compared to MMTV-neu/p27(+/+) glands. These results suggest that p27(+/-) mammary epithelium may be more susceptible to oncogene-induced tumorigenesis, whereas p27-null glands, due to severely impaired cyclin D1/Cdk4 function, are more resistant to transformation.
Muraoka
Rebecca S
RS
Department of Cancer Biology, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Lenferink
Anne E G
AE
Law
Brian
B
Hamilton
Elizabeth
E
Brantley
Dana M
DM
Roebuck
L Renee
LR
Arteaga
Carlos L
CL
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000235:genetics; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000473:pathology; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D005434:Flow Cytometry; D017353:Gene Deletion; D018628:Gene Dosage; D008321:Mammary Glands, Animal / Q000378:metabolism / Q000473:pathology; D008325:Mammary Neoplasms, Experimental / Q000235:genetics / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000172:deficiency* / Q000235:genetics
D018797:Cell Cycle Proteins; D019938:Cyclin D1; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D018719:Erb-b2 Receptor Tyrosine Kinases; D025521:Tumor Suppressor Proteins; C493961:Cdkn1b protein, mouse; C495902:Cdk4 protein, mouse