Anti-PPFIA1 (aa 574-604) polyclonal antibody

Human PPFIA1 (also known as LIP.1 or Liprin alpha1) gene, located within CCND1-FGF4-EMS1 amplicon at human chromosome 11q13.3, encodes KIF I A-binding protein, which is implicated in trafficking of LAR subfamily PTPases and AMPA-type glutamate receptors. Human PPFIA4 (AF034801) and rat Ppfia4 (AY057064) are 5'-truncated partial cDNAs, and the complete coding sequence of PPFIA4 ortholog of any species remained to be identified. Here, we determined the complete coding sequence of human PPFIA4 gene by using bioinformatics. Exons 1-12 of PPFIA4 gene were located within human genome sequence AC096632.3, while exons 11-29 within AL451082.6. PPFIA4-MYOG locus (human chromosome 1q32.1) was paralogous to PPFIA2-LIN7A-MYF5-MYF6 locus (12q21.31), which was also paralogous to PPFIA3-LIN7B locus (19q13.41). PPFIA4 (1186 aa) showed 70.9%, 67.1%, and 61.8% total-amino-acid identity with PPFIA2, PPFIA1, and PPFIA3, respectively. PPFIA family members consist of PFIH1, PFIH2, PFIH3, PFIH4 domains and three SAM (Sterile alpha motif) domains. C-terminal binding domain for GRIP proteins (VRTYSC motif) was present in PPFIA1, PPFIA2 and PPFIA3, but not in PPFIA4. Bipartite nuclear localization signal was included within PFIH4 domain. PFIH2 domain was identical to ERM or Smc domain. The region spanning PFIH2-PFIH3 domains is the binding domain for KIF1A. The region spanning SAM1-SAM3 domains is the binding domain for LAR subfamily PTPases and PPFIBP (Liprin beta) family proteins. This is the first report on comprehensive characterization of PPFIA4 belonging to the PPFIA family of kinesin-cargo linkers.

Background: PPFIA1 is located at the 11q13 region commonly amplified in cancer. The protein liprin-alpha 1 encoded by PPFIA1 contributes to the adhesive and invasive structures of cytoskeletal elements and is located at the invadosomes in cancer cells. However, the precise mechanism of liprin-alpha 1 function in cancer progression has remained elusive. Methods: Invasion regulating activity of liprin-alpha 1 was examined by analyzing the functions of squamous cell carcinoma of head and neck (HNSCC) cell lines in three-dimensional collagen I after RNAi mediated gene knockdown. Transcriptome profiling and Gene Set Enrichment Analysis from HNSCC and breast cancer cells were used to identify expression changes relevant to specific cellular localizations, biological processes and signaling pathways after PPFIA1 knockdown. The significance of the results was assessed by relevant statistical methods (Wald and Benjamini-Hochberg). Localization of proteins associated to liprin-alpha 1 was studied by immunofluorescence in 2D and 3D conditions. The association of PPFIA1 amplification to HNSCC patient survival was explored using The Cancer Genome Atlas data. Results: In this study, we show that liprin-alpha 1 regulates biological processes related to membrane microdomains in breast carcinoma, as well as protein trafficking, cell-cell and cell-substrate contacts in HNSCC cell lines cultured in three-dimensional matrix. Importantly, we show that in all these cancer cells liprin-alpha 1 knockdown leads to the upregulation of transmembrane protein CD82, which is a suppressor of metastasis in several solid tumors. Conclusions: Our results provide novel information regarding the function of liprin-alpha 1 in biological processes essential in cancer progression. The results reveal liprin-alpha 1 as a novel regulator of CD82, linking liprin-alpha 1 to the cancer cell invasion and metastasis pathways.