Recombinant Human LRIG1 Protein, CF

LRIG1 is a 145 kDa leucine-rich repeat (LRR) and Ig-like domain-containing single-pass transmembrane glycoprotein. It has been shown to suppress tumor growth, regulate tissue homeostasis, and maintain stem cell quiescence (1-5). Human LRIG1 is synthesized with a 34 amino acid (aa) signal sequence, a 759 aa extracellular domain (ECD), a 21 aa transmembrane sequence, and a 278 aa cytoplasmic region. The LRIG1 ECD contains three C-type Ig-like domains as well as fifteen LRRs that are flanked by cysteine-rich regions (6, 7). The ECD of human LRIG1 shares 90% and 88% aa identity with the ECD of mouse and rat LRIG1, respectively. LRIG1 shares 45-50% aa identity with its mammalian paralogs, LRIG2 and LRIG3. LIRG1 is expressed widely throughout mouse and human tissues, including the liver, brain, stomach, small intestine, skeletal muscle, cornea, and hair follicle (3, 6, 8). LRIG1 functions as a tumor suppressor by controlling cell proliferation through the negative regulation of the EGF family of receptor tyrosine kinases. Specifically, the ECD of LRIG1 binds to EGF R, ErbB2, ErbB3, and ErbB4, inducing receptor ubiquitination and degradation (9, 10). LRIG1 expression, which is often dysregulated in human cancers, is a prognostic indicator of cancer development and relapse; decreased LRIG1 is associated with an increase in recurrence and mortality for a variety of cancers including breast, uterine, head-and-neck, glioma, prostate, and squamous cell (2, 11-13). Tissue homeostasis and stem cell dormancy is also thought to be modulated by the actions of LRIG1 on cell proliferation (14).