Most oral leukoplakic lesions represent hyperkeratotic epithelium (benign), dysplasia, or squamous cell carcinoma. The lesions must be biopsied and examined microscopically for diagnosis. But, morphology alone does not answer the question about which non-invasive lesions will progress to cancer. The uncertainty of whether a given lesion will progress to cancer or not often compromises the use of the best therapeutic option which is complete excision because of the complications of surgery. So, the question to be answered by the proposed research is, """"""""Will a given leukoplakic oral lesion likely progress to cancer?"""""""" The research will begin to answer the question by examining the genomic sequences of pp32r1 (GenBank AF008216) present within existing biopsy specimens. In a pilot sequencing survey of the pp32r1 gene in tobacco-associated, oral, leukoplakic lesions, the principal investigator found a mutant, growth-accelerating pp32r1 gene in an oral squamous cell carcinoma. The first specific aim of the project is to amplify and sequence the pp32r1 gene within formalin-fixed, paraffin embedded specimens of oral leukoplakia. The basic hypothesis is that certain neoplastic cells within those lesions contain mutations encoding non-conservative amino acid substitutions within residues 136-172. These mutations define malignant cells long before they clonally enlarge and form a clinical cancer. Another question concerns the discrete molecular activities of mutant, carcinoma-associated PP32R1 proteins as they accelerate cellular growth. The pp32r1 gene is a member of a family of genes that encode proteins with myriad activities. All the family members contain N-terminal domains with leucine-rich repeats that form adapter sites for protein-protein interactions. And, all the family members contain extremely acidic C-terminals that form alternative adapter sites for protein-protein interactions by ionic forces. Another common physical characteristic is that other family members, particularly PP32, often appear in nature bound to other intracellular proteins. It is thought that mutant, carcinoma-associated, growth-accelerating PP32R1s differentially bind intracellular proteins in comparison to wild-type PP32R1s and other members of the PP32 family. The resultant abnormal macromolecular complexes change cellular homeostasis in ways that accelerate growth. The second specific aim of the project is co-immunoprecipitation of PP32R1 binding proteins, separation of the binding partners by 2-dimensional (2D) gel electrophoresis, and identification by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. Identification of the intracellular protein ligands will provide a specific functional context for mutant PP32R1S.
