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Cell cycle-dependent regulation of p185neu: a relationship between disruption of this regulation and transformation
N Kiyokawa1, D H Yan, M E Brown
1Department of Tumor Biology, University of Texas M.D. Anderson Cancer Center Houston 77030.
Abstract:
Structure and function of p185neu receptor tyrosine kinase were found to be regulated in a cell cycle-dependent manner. In M phase, p185neu is hyperphosphorylated at serine and/or threonine residues. The phosphotyrosine [Tyr(P)] content of p185neu is at its highest level in G0/G1 phase, decreases through S and G2 phases, and reaches its lowest level in M phase. Phospholipase C-gamma (PLC-gamma) and GTPase-activating protein (GAP), substrates of p185neu, also have a similar profile of Tyr(P) content during the cell cycle. These results, along with in vitro immune complex kinase assays, suggest that the tyrosine kinase activity of p185neu is least active in M phase. Interestingly, the mutation-activated neu oncogene (neu*)-encoded protein product, p185neu* escaped from cell cycle regulation. Taken together, we demonstrate in this report that the structure and function of p185neu are regulated in a cell cycle-dependent manner, yet p185neu* escapes from this regulation and remains active through the cell cycle. Disruption of this cell cycle regulation may define a mechanism for p185neu*-mediated cellular transformation.
Insights
The p185neu receptor tyrosine kinase
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- The p185neu receptor tyrosine kinase plays a critical role in cellular signaling.
- Its activity is known to be modulated by various cellular processes.
- Understanding its regulation is key to comprehending normal cell function and disease states.
Purpose of the Study:
- To investigate the cell cycle-dependent regulation of p185neu structure and function.
- To determine how oncogenic mutations affect this regulation.
- To elucidate potential mechanisms of oncogenesis driven by deregulated p185neu.
Main Methods:
- Analysis of p185neu phosphorylation (serine/threonine and tyrosine) across cell cycle phases.
- Quantification of phosphotyrosine (Tyr(P)) content in p185neu and its substrates (PLC-gamma, GAP).
- In vitro immune complex kinase assays to assess tyrosine kinase activity.
- Comparison of wild-type p185neu with mutation-activated neu* protein.
Main Results:
- p185neu exhibits cell cycle-dependent regulation, with highest phosphotyrosine levels in G0/G1 and lowest in M phase.
- Tyrosine kinase activity of p185neu is lowest during M phase.
- Substrates like PLC-gamma and GAP show similar cell cycle-dependent phosphotyrosine profiles.
- The oncogenic p185neu* protein escapes cell cycle regulation, remaining active throughout.
Conclusions:
- p185neu's structure and function are tightly regulated by the cell cycle.
- This regulation is disrupted in the oncogenic neu* variant, leading to constitutive activity.
- Loss of cell cycle control over p185neu activity may drive cellular transformation and cancer development.