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Growth activation of resting cells: induction of balanced and imbalanced growth
Abstract:
Little is known about how mitogenic factors generate growth regulatory signals and how these are mediated within the cell. We have developed three different types of mitogenic stimuli in order to identify the possible existence of common denominators in a complex and perhaps pleiotypic signal-response system. 3T3 cells, starved to quiescence by reducing the serum content of the culture medium 100-fold, can be irreversibly committed to undergo DNA replication and mitosis in a serum-free medium after an initial exposure of short duration to (a) serum factors and cholesterol, (b) a relative excess of glutamine, or (c) alkaline pH. Cells stimulated by any of these procedures, and subsequently incubated in serum-free Dulbecco's modified Eagle's medium (DMEM) undergo DNA replication and mitosis in the absence of concomitant cellular enlargement (imbalanced growth). However, cellular enlargement is induced after the initial mitogenic stimuli (a, b, and c, as described previously) if the cells are subsequently incubated in DMEM containing greater than or equal to 0.5% serum, supraphysiological concentrations of insulin, or normal concentrations of somatomedin C.
Insights
Mitogenic factors trigger cell division (DNA replication and mitosis) through common signaling pathways. Subsequent cell enlargement requires specific growth factors like serum, insulin, or somatomedin C.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Understanding how mitogenic factors initiate cellular growth signals is crucial.
- The precise mechanisms of signal transduction in response to mitogens are not fully elucidated.
- Identifying common signaling pathways in response to diverse stimuli is key to understanding cell growth regulation.
Purpose of the Study:
- To investigate potential common denominators in the signal-response system of mitogenic factors.
- To identify shared pathways activated by distinct mitogenic stimuli.
- To differentiate signals for cell division from signals for cell growth.
Main Methods:
- Utilized 3T3 cells, induced to quiescence by serum reduction.
- Applied three distinct mitogenic stimuli: serum factors/cholesterol, excess glutamine, and alkaline pH.
- Incubated stimulated cells in serum-free or low-serum Dulbecco's modified Eagle's medium (DMEM) with varying supplements.
Main Results:
- Short exposure to any of the three stimuli committed quiescent 3T3 cells to DNA replication and mitosis in serum-free medium.
- Cells underwent DNA replication and mitosis without significant cell enlargement (imbalanced growth) in serum-free DMEM.
- Cellular enlargement was observed when stimulated cells were subsequently incubated in DMEM with ≥0.5% serum, supraphysiological insulin, or normal somatomedin C.
Conclusions:
- Distinct mitogenic stimuli can converge on common pathways to induce cell division.
- Separate signaling pathways regulate cell division versus cell enlargement.
- Growth factors like insulin and somatomedin C, along with serum components, are essential for mediating cellular enlargement post-mitogenic stimulation.