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STRA6 in Cancer and Diabetes
STRA6 (STimulated by Retinoic Acid-6) - is a membrane receptor protein on the cell surface thought to facilitate the uptake of retinol from the RBPs.
STRA6 was over expressed up to 172-fold in 14 out of 14 human colorectal tumors relative to normal colon tissue (Szeto et al., 2001).
https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/stra6
Interestingly, it has been reported that plasma level of RBP increases in obese mice and humans and that the elevated serum levels of the protein markedly suppress insulin responses (9). Thus, RBP may link obesity and insulin resistance.
But, it turns out that STRA6 is actually not needed for uptake of retinol.
Our studies provide several lines of evidence that establish that, with the exception of the eye, STRA6 is not critical for maintaining ROH (retinol) availability in tissues that express it. (i) The retinoid content of tissues is indistinguishable in Stra6-null and WT mice fed a regular chow diet. (ii) Stra6-null fetuses recovered from dams fed a VADD do not exhibit any hallmarks of fetal VAD syndrome.
Source:
The STRA6 Receptor Is Essential for Retinol-binding Protein induced Insulin Resistance but Not for Maintaining Vitamin A Homeostasis in Tissues Other Than the Eye
https://www.jbc.org/article/S0021-9258(20)45207-X/fulltext
So, what is STRA6 really? Is it just another defective protein produced by the cell when exposed to RA poisoning? It sure looks like it.
What are the consequences of cells wrongly producing large numbers of STRA6? Insulin resistance and diabetes for starters.