Scavenger receptor class B type 1 (SRB1) also known as SR-BI is a protein that in humans is encoded by the SCARB1gene.[5] SR-BI functions as a receptor for high-density lipoprotein.[6]
SR-BI is crucial in carotenoid and vitamin E uptake in the small intestine.[8][9] SR-B1 is upregulated in times of vitamin A deficiency and downregulated if vitamin A status is in the normal range.[10]
In melanocytic cells SCARB1 gene expression may be regulated by the MITF.[11]
Species distribution
SR-BI has also been identified in the livers of non-mammalian species (turtle, goldfish, shark, chicken, frog, and skate), suggesting it emerged early in vertebrate evolutionary history. The turtle also seems to upregulate SR-BI during egg development, indicating that cholesterol efflux may be at peak levels during developmental stages.[12]
Although malignant tumors are known to display extreme heterogeneity, overexpression of SR-B1 is a relatively consistent marker in cancerous tissues. While SR-B1 normally mediates the transfer of cholesterol between high-density lipoproteins (HDL) and healthy cells, it also facilitates the selective uptake of cholesterol by malignant cells. In this way, upregulation of the SR-B1 receptor becomes an enabling factor for self-sufficient proliferation in cancerous tissue.[14][15]
SR-B1 mediated delivery has also been used in the transfection of cancer cells with siRNA, or small interfering RNAs. This therapy causes RNA interference, in which short segments of double stranded RNA acts to silence targeted oncogenes post-transcription. SR-B1 mediation reduces siRNA degradation and off-target accumulation while enhancing delivery to targeted tissues. In "metastatic and taxane-resistant models of ovarian cancer, rHDL-mediated siren delivery improved responses.[16]
Interactive pathway map
Click on genes, proteins and metabolites below to link to respective articles.[§ 1]
^Rhainds D, Brissette L (January 2004). "The role of scavenger receptor class B type I (SR-BI) in lipid trafficking. defining the rules for lipid traders". The International Journal of Biochemistry & Cell Biology. 36 (1): 39–77. doi:10.1016/s1357-2725(03)00173-0. PMID14592533.
^van Bennekum A, Werder M, Thuahnai ST, Han CH, Duong P, Williams DL, et al. (March 2005). "Class B scavenger receptor-mediated intestinal absorption of dietary beta-carotene and cholesterol". Biochemistry. 44 (11): 4517–25. doi:10.1021/bi0484320. PMID15766282.
^Blaner WS (2020). "Vitamin A". In BP Marriott, DF Birt, VA Stallings, AA Yates (eds.). Present Knowledge in Nutrition, Eleventh Edition. London, United Kingdom: Academic Press (Elsevier). pp. 73–92. ISBN978-0-323-66162-1.
^Duggan AE, Marie RS, Callard IP (April 2002). "Expression of SR-BI (Scavenger Receptor Class B Type I) in turtle (Chrysemys picta) tissues and other nonmammalian vertebrates". The Journal of Experimental Zoology. 292 (5): 430–4. doi:10.1002/jez.10067. PMID11857477.
Williams DL, Temel RE, Connelly MA (November 2000). "Roles of scavenger receptor BI and APO A-I in selective uptake of HDL cholesterol by adrenal cells". Endocrine Research. 26 (4): 639–51. doi:10.3109/07435800009048584. PMID11196441. S2CID21441940.
Krause BR, Auerbach BJ (March 2001). "Reverse cholesterol transport and future pharmacological approaches to the treatment of atherosclerosis". Current Opinion in Investigational Drugs. 2 (3): 375–81. PMID11575708.
Connelly MA, Williams DL (June 2004). "Scavenger receptor BI: a scavenger receptor with a mission to transport high density lipoprotein lipids". Current Opinion in Lipidology. 15 (3): 287–95. doi:10.1097/00041433-200406000-00008. PMID15166784. S2CID24035736.
Phillips RW (1978). "The new era in restorative dental materials". Operative Dentistry. 1 (1): 29–35. PMID1076467.
Johnson MS, Svensson PA, Borén J, Billig H, Carlsson LM, Carlsson B (June 2002). "Expression of scavenger receptor class B type I in gallbladder columnar epithelium". Journal of Gastroenterology and Hepatology. 17 (6): 713–20. doi:10.1046/j.1440-1746.2002.02776.x. PMID12100619. S2CID21584794.
