Connection between skin pigment and likelihood of skin cancer might be more complex than previously thought.

by SchwerdtfegerK on March 23, 2017 - 11:14am

“Human melanocortin 1 receptor (MC1R) gene variants alter melanoma cell growth and adhesion to extracellular matrix” examines the long-known connection between mutations in the gene MC1R and predisposition to skin cancer. This gene is responsible for the production of melanin, a protein which affects external pigmentation, in particular affecting the hair and skin color of humans. Faulty expressions of this gene often result in such phenotypical features as red hair, freckles, and poor tanning under higher amounts of sunlight, and the genotypes for these traits are inherited through an autosomal recessive pattern, meaning that an atypical allele of said gene must be inherited from both parents.

It is commonly assumed that those with a faulty MC1R gene will be at higher risk of developing melanoma, a pigmented skin cancer, from UV exposure than would those with a typical MC1R allele, and that those with darker pigmentation ae at less risk for melanoma than those with lighter pigmentation, by means of differing melanin levels. However, what this titular study seems to find is that the correlation is not so cut and dry. While the study had acknowledged that there is a correlation between the presence of recessive MC1R variants and increased predisposition to skin cancer, it was also found that there were alleles of this gene that resulted in increased risk for melanoma that were independent from variations in pigmentation.

It is important to note that the full term “melanocortin 1 receptor” refers to the gene ultimately responsible for the production of melanin in tissue cells, but it also is used to refer to the protein that it encodes for. To avoid potential confusion in this critique, I will reference the original study’s technique of referring to the gene as MC1R and the encoded protein as Mc1r.

The study tested the effects of Mc1r variants on cloned melanoma cells by introducing various strands of Mc1r to said melanoma cells. What the study had found was that certain varieties of the Mc1r protein coincided with an increased risk for the development of melanomas, but that these proteins did not necessarily coincide with the more typical phenotypical expressions of MC1R mutations. That is to say, there were certain proteins that, while they did not result in red hair, freckles or poor tanning, triggered a similar increased risk of skin cancer similarly to those with the aforementioned phenotypes.
Those who conducted the study had admitted that the methodology for this consisted of recording skin/pigment type based on historical data reported by the subjects, which could have been erroneous to an indeterminate degree, due to the difficulty any one individual would have reporting their total ancestral sum. The data seemed consistent enough, however, that it could be comfortably inferred that Mc1r proteins have a more complex role than to simply control external pigmentation.

 

I feel that the abstract to this study, in its original form, is cohesive to those who are already familiar with the terminology being discussed. There is the potential for those who are unfamiliar with the terminology utilized in this study to be discouraged, but it would also most likely be people already familiar with said terminology reading this in the first place.

The issue of human pigmentation is of some interest to me, admittedly a smaller subset of the greater topic of human genetic variation. I like to understand the connection between surface variations in human appearance and the biological consequences that may come along with them, which is usually minimal, at most.

Comments

Well hello…you do look a bit sunburned I must say. Having trouble with your melanocyte-stimulating hormone (MSH) or melanocortin 1 receptor? Not me, fortunately. Just look at my tan! But you say it is possible, even for those who do not express the phenotypic traits associated with faulty expression of the gene to be at risk for melanoma? Do you mean at greater risk than the normal population? Hmmm. I’m putting my shirt back on and am scurrying back to the shade. I just opened my laptop (good WIFI at the beach hotspot) and found an article entitled, “MC1R melanocortin 1 receptor [ Homo sapiens (human) ]”
From what I’m reading, it seems that MSH must bind to its receptor to activate it so it stimulates “eumelanin” synthesis. Apparently eumelanin is photoprotective but the second type of melanin, red pheomelanin, can contribute to UV induced skin damage. It generates free radicals after exposure to UV radiation.

I wonder how I can get tested for this particular allele…But I’ve heard bad things about 23sunburnedandme.com. I guess I should be careful. I have read articles about the increased levels of UVB in recent years and how it’s related to ozone levels etc.…
I guess my sun tanning days are over. Besides, I don’t want to look like I work all day in the sun do I? Oops, yes I do.

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