Related Experiment Videos
Isolation and characterization of a variant of B16-mouse melanoma resistant to MSH growth inhibition
Abstract:
A variant of B-16 F1 mouse melanoma was selected for its ability to survive and replicate in the presence of melanocyte-stimulating hormone (MSH). Although the variant (MR-4) was completely resistant to growth inhibition of MSH, cyclic AMP was still able to block cell replication. Tyrosinase activity in MR-4 cells was considerably lower than in B-16 F1 cells. MSH induced a two fold to three-fold increase in tyrosinase activity in both cell types, but the absolute activity in MR-4 remained significantly less than in the parental cells. MR-4 cells were also found to have a markedly depressed cyclic AMP-dependent protein kinase activity relative to B-16 F1 cells. The protein kinase from both cell types was stimulated by cyclic AMP, but the level of MR-4 kinase activity at maximal cyclic AMP concentrations remained considerably lower than B-16 F1 kinase activity under the same conditions. In both cell types adenylate cyclase activity was markedly stimulated by MSH. When equal numbers of viable F1 and MR-4 cells were injected subcutaneously into C57/B1 mice, the MR-4 cells formed tumors earlier and killed the host sooner than the parental F1 cells. We conclude that the biochemical alteration which allows MR-4 cells to replicate in the presence of MSH is a low level of tyrosinase activity, which in turn may be the result of low cyclic AMP-dependent protein kinase activity.
Insights
A melanoma variant (MR-4) resistant to melanocyte-stimulating hormone (MSH) showed lower tyrosinase and cyclic AMP-dependent protein kinase activity. This biochemical alteration contributes to faster tumor growth in mice.
Area of Science:
- Cancer Biology
- Biochemistry
- Cellular Signaling
Background:
- Melanoma cells exhibit varying responses to melanocyte-stimulating hormone (MSH).
- Understanding MSH resistance mechanisms is crucial for melanoma treatment.
Purpose of the Study:
- To investigate the biochemical basis of MSH resistance in a B-16 F1 mouse melanoma variant (MR-4).
- To compare the activity of key enzymes and signaling molecules between MSH-resistant and parental melanoma cells.
Main Methods:
- Selected and characterized MSH-resistant melanoma variant (MR-4).
- Assessed tyrosinase activity, cyclic AMP levels, and cyclic AMP-dependent protein kinase activity.
- Measured adenylate cyclase activity.
- In vivo tumor growth studies in C57/B1 mice.
Main Results:
- MR-4 cells were resistant to MSH-induced growth inhibition but responsive to cyclic AMP.
- MR-4 cells displayed significantly lower basal and MSH-induced tyrosinase activity compared to parental B-16 F1 cells.
- MR-4 cells exhibited reduced cyclic AMP-dependent protein kinase activity.
- MSH stimulated adenylate cyclase in both cell types.
- MR-4 tumors grew faster and were more lethal in mice.
Conclusions:
- A biochemical alteration, specifically low tyrosinase activity, enables MR-4 cells to replicate despite MSH presence.
- This low tyrosinase activity may stem from diminished cyclic AMP-dependent protein kinase activity.
- The MR-4 variant demonstrates increased tumorigenicity, highlighting the role of these biochemical changes in melanoma progression.