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Control of pigment production in mouse melanoma cells in vitro. Evocation and maintenance
Abstract:
A clonally derived amelanotic melanoma cell line repeatedly has been forced to produce pigment by the inhibitor of DNA synthesis, I-beta-D-arabinofuranosylcytosine (ara-C) at sublethal levels. One ara-C-derived melanotic line has been cloned, and has continued to produce pigment for 2 years on normal medium. The inhibitor is most effective when administered to synchronized cells in four pulses on successive days at 1.8 x 10(-5)M during the S phase of the cell cycle. Colcemid at a sublethal concentration, and growth on medium solidified with agar also evoked pigment production in this line, but a large number of other inhibitors of biosynthetic processes did not, under the conditions tested. The melanotic lines are active producers of tyrosinase (DOPA oxidase), whereas the amelanotic line produces an inhibitor of tyrosinase activity. Both enzyme and inhibitor are labile at 4 degrees C and -20 degrees C, and decay of the inhibitor in homogenates of amelanotic cells reveals a low level of residual DOPA oxidase activity. The mean population doubling time of a cloned melanotic line is 23 hr, and that of a cloned amelanotic line 16.5 hr. A similar decrease in rate of growth is found in other melanotic lines and is believed to be a significant factor in maintaining this differentiated function. Rapid growth may be related to the production of an inhibitor by the amelanotic cells.
Insights
Inhibiting DNA synthesis with I-beta-D-arabinofuranosylcytosine (ara-C) induced pigment production in amelanotic melanoma cells. These induced melanotic cells stably produced pigment, suggesting a potential for differentiation therapy.
Area of Science:
- Cell Biology
- Cancer Research
- Biochemistry
Background:
- Amelanotic melanoma cells lack pigment production.
- Inducing differentiation in cancer cells is a therapeutic goal.
Purpose of the Study:
- To investigate methods for inducing pigment production in amelanotic melanoma cells.
- To characterize the resulting melanotic cell lines and their properties.
Main Methods:
- Treatment of amelanotic melanoma cells with I-beta-D-arabinofuranosylcytosine (ara-C) at sublethal doses.
- Cloning of induced melanotic cell lines and long-term culture.
- Analysis of tyrosinase activity and inhibitor presence in cell lines.
- Comparison of growth rates between amelanotic and melanotic cell lines.
Main Results:
- Sublethal I-beta-D-arabinofuranosylcytosine (ara-C) treatment induced stable pigment production in amelanotic melanoma cells.
- Induced melanotic cell lines produced tyrosinase (DOPA oxidase), while amelanotic cells produced a tyrosinase inhibitor.
- Melanotic cell lines exhibited slower growth rates (23 hr doubling time) compared to amelanotic lines (16.5 hr doubling time).
- Colcemid and agar medium also induced pigment, but other inhibitors did not.
Conclusions:
- Inhibitors of DNA synthesis can induce differentiation in amelanotic melanoma cells.
- Stable pigment production and altered growth rates are characteristic of induced melanotic melanoma cells.
- Tyrosinase activity and its inhibition play a role in melanoma cell differentiation and growth.