Assessing SPP1/Osteopontin (OPN) Splice Variants and Their Association to Nonmelanoma Skin Cancer by Absolute Quantification: Identification of OPN-5 Subvariants and Their Protein Coding Potential

The study evaluated whether SPP1/osteopontin (OPN) splice variants are differentially expressed in nonmelanoma skin cancer compared to normal skin. The absolute number of mRNA molecules of OPN-a predominated in nonmelanoma skin cancer and in normal skin compared to OPN-b, OPN-c, and OPN-5. Furthermore, mRNAs of OPN-a, OPN-b, and OPN-c were expressed in higher levels in cutaneous squamous cell carcinomas and basal cell carcinomas relative to normal skin. Additionally, in normal skin, OPN-5 had higher expression than OPN-b and OPN-c, and OPN-c in nonmelanoma skin cancer consisted of subvariants, which were cloned and analyzed for protein expression.