A tyrosine residue on β4 integrin endodomain plays a key role in epidermal tumorigenesis

Summary: Abstract Body: β4 integrin is crucial for squamous cell carcinoma (SCC) tumor formation. However, the mechanisms underlying β4 integrin-mediated SCC tumorigenesis remain unclear. To clarify β4 integrin’s functional role in SCC tumorigenesis, we overexpressed mutant β4 integrin cDNAs in β4 integrin null primary junctional epidermolysis bullosa (JEB) keratinocytes and studied the ability of these engineered cells to support SCC tumor formation in immunodeficient mice after Ras/IκB transformation. We also generated β4 integrin knockouts in human SCC line to complement the JEB keratinocyte studies. Phospho-mimic substitution of the tyrosine 1642 residue with aspartic acid (1642D) in β4 null JEB cells after Ras/IκB transformation as well as in human ITGB4 KO SCC cell line promoted hyperproliferation by nuclear translocalization of phospho-JNK and PI3K signaling, resulting in vivo human SCC tumor progression. On the contrary Phospho-ablative substitution of the tyrosine 1642 residue with phenylalanine (1642F) demonstrated hypoproliferation, reduced PI3k activity and an almost total lack of tumor growth. β4 integrin AP-MS indicated strong association with Rac1 pathway proteins pointing towards leading pathway for characteristic hyperproliferation and invasion. Further studies with β4 integrin null JEB cells expressing mutant β4 cDNAs demonstrated that EGF stimulation promoted tyrosine 1642 phosphorylation via a signaling cascade which appeared to be regulated by Fyn kinase. Overexpression of a constitutively active PI3K p110 submit mutant restored tumor formation in 1642F expressing JEB keratinocytes following Ras/IκB transformation. Binding of plectin to β4 integrin appeared to antagonize β4 integrin intramolecular association which likely facilitates tyrosine 1642 phosphorylation. These findings identify new mechanisms for β4 integrin dependent SCC tumor progression and point to the β4 integrin 1642 tyrosine phosphorylation as a target for novel cancer therapies. Pragya Tripathi¹, MP Marinkovich¹, Yoshi Kariya² 1. Dermatology, Stanford University School of Medicine, Stanford, CA, United States. 2. Fukushima Kenritsu Ika Daigaku Igakubu Daigakuin Igaku Senko, Fukushima, Fukushima Prefecture, Japan. UV Biology/Injury and Non-melanoma Cancers