ABSTRACT
Transforming growth factor-beta1 (TGF-beta1) inhibits cell growth in susceptible cells by interacting with a family of protein kinases that control cell cycle progression. In the present study, we investigated the effects of TGF-beta1 on cyclin D1 expression and activity in COLO-357 human pancreatic cancer cells. TGF-beta1 increased cyclin D1 mRNA and protein levels. Nuclear runoff transcription and protein synthesis inhibition by cycloheximide revealed that this increase was, in part, due to increased cyclin D1 mRNA synthesis. Despite its stimulatory effects on cyclin D1 levels, TGF-beta1 inhibited cyclin D1-associated kinase activity and the growth of COLO-357 cells. Furthermore, suppression of cyclin D1 expression with a cyclin D1 antisense cDNA resulted in loss of TGF-beta1-mediated growth inhibition in association with reduced induction of cyclin D1, p21(C)(ip)(1) and plasminogen activator inhibitor-1 (PAI-1). Concomitantly, there was a marked decrease in the levels of the type I TGF-beta receptor (TbetaRI). Our findings suggest that in some cell types cyclin D1 expression may be important for TGF-beta1-mediated signaling and that cyclin D1 may be involved in the transcriptional regulation of TbetaRI.
Subject(s)
Activin Receptors, Type I , Cyclin D1/antagonists & inhibitors , Cyclin D1/biosynthesis , Pancreatic Neoplasms/metabolism , Protein Serine-Threonine Kinases/biosynthesis , Receptors, Transforming Growth Factor beta/biosynthesis , Transforming Growth Factor beta/pharmacology , Cell Division/drug effects , Cyclin D1/genetics , Cyclin-Dependent Kinase Inhibitor p21 , Cyclin-Dependent Kinases/antagonists & inhibitors , Cyclins/biosynthesis , Cyclins/genetics , Cyclins/metabolism , Dose-Response Relationship, Drug , Down-Regulation/drug effects , Growth Inhibitors/pharmacology , Humans , Insulin-Like Growth Factor I/pharmacology , Oligonucleotides, Antisense/biosynthesis , Oligonucleotides, Antisense/genetics , Oligonucleotides, Antisense/pharmacology , Pancreatic Neoplasms/pathology , RNA, Messenger/biosynthesis , RNA, Messenger/metabolism , Receptor, Transforming Growth Factor-beta Type I , Transforming Growth Factor beta/physiology , Tumor Cells, Cultured , Up-Regulation/drug effectsABSTRACT
Insulin receptor substrate-2 (IRS-2) is a multisite docking protein implicated in mitogenic signaling after activation of the insulin and insulin-like growth factor (IGF)-I receptors. In the present study, we characterized IRS-2 expression and function in human pancreatic cancer. IRS-2 mRNA and protein were expressed in ASPC-1 and COLO-357 human pancreatic cancer cell lines. Insulin, IGF-I, and IGF-II enhanced the growth of both cell lines, stimulated tyrosine phosphorylation of IRS-2, and increased IRS-2-associated phosphatidylinositol (PI) 3-kinase activity. The mitogenic effects of insulin, IGF-I, and IGF-II were markedly attenuated by the PI 3-kinase inhibitor LY 294002. Northern blot analysis of total RNA extracted from normal and cancerous tissues revealed that IRS-2 mRNA levels were increased in the cancer tissues (P = 0.032). In the normal pancreas, IRS-2 immunoreactivity was present at low levels in some ductal and acinar cells and at moderate levels in a heterogeneous pattern in all of the endocrine islets. In the pancreatic cancers, IRS-2 was abundant in the ductal-like cancer cells. These findings indicate that IRS-2 is overexpressed in human pancreatic cancer and suggest that it may contribute to enhanced mitogenic signaling via the PI 3-kinase pathway, thereby leading to excessive growth stimulation in this malignancy.
Subject(s)
Gene Expression Regulation, Neoplastic/physiology , Growth Substances/pharmacology , Pancreas/metabolism , Pancreatic Neoplasms/metabolism , Phosphoproteins/genetics , Colonic Neoplasms , Gene Expression Regulation, Neoplastic/drug effects , Growth Substances/physiology , Humans , Insulin/pharmacology , Insulin Receptor Substrate Proteins , Insulin-Like Growth Factor I/pharmacology , Insulin-Like Growth Factor II/pharmacology , Intracellular Signaling Peptides and Proteins , Pancreas/cytology , Pancreatic Neoplasms/genetics , Pancreatic Neoplasms/pathology , Phosphatidylinositol 3-Kinases/metabolism , Phosphoproteins/biosynthesis , Protein Biosynthesis , RNA, Messenger/biosynthesis , Transcription, Genetic , Tumor Cells, CulturedABSTRACT
Cyclin D 1 belongs to a family of protein kinases that have been implicated in cell cycle regulation. In the present study we characterized cyclin D1 expression in 6 cultured human pancreatic cancer cell lines and in normal and cancerous human pancreatic tissues. A 4.4-kb cyclin D1 mRNA transcript was present in all cell lines and in all pancreatic tissues. Cyclin D1 mRNA levels were 2.1-fold higher in the pancreatic cancers than in normal pancreatic tissues (p < 0.0002). Cancer patients with lower cyclin D1 levels (n=16) had a median survival of 15.5 months whereas patients with higher levels (n=16) had a median survival of 6.5 months (p < 0.007). These data indicate that cyclin D1 expression may serve as a predictor of postoperative survival in pancreatic cancer patients, and raise the possibility that treatment modalities blocking cyclin D1 activity may have a future role in the therapy of these patients.
