IGF1 and squamous cell carcinoma: IGF-1 has been shown to increase transepithelial electrical resistance (a measure of barrier function) by regulating occludin and claudin-3 in submandibular gland cells [51], zona occludens (ZO)-1 in A431 human epidermoid carcinoma cells [52] and claudin-1 in osteoblast cells [53].