Journal: International Journal of Molecular Sciences

Article Title: PIMT Binding to C-Terminal Ala459 of CAIX Is Involved in Inside-Out Signaling Necessary for Its Catalytic Activity

doi: 10.3390/ijms21228545

Figure Lengend Snippet: C -terminal amino acid Ala459 residue cooperates in the regulation of CAIX catalytic function: ( a ) Immunoblot analysis of cell lysates from C33a cells transfected with mock control, CAIX wild type (wt) or mutant (A459G) cultured 48 h in hypoxia. CAIX was detected using mouse monoclonal antibody M75 diluted 1:10 and β-actin was detected using mouse monoclonal antibody (CS3700, Cell Signaling Technology, Danvers, Massachusetts) diluted 1:5000. HRP-conjugated anti-mouse antibody (Dako Agilent, Santa Clara, California) diluted 1:5000 was used as a secondary antibody. ( b ) Fluorescence staining of CAIX in non-fixed and non-permeabilized C33a-CAIX wild type as well as A459G transfectants measured by flow cytometry. CAIX was detected using PG-domain specific mouse monoclonal antibody M75 diluted to 1 µg/mL and AlexaFluor 488-conjugated anti-mouse secondary antibody (Invitrogen, Carlsbad, California) diluted 1:1000. Results clearly demonstrate plasma membrane localization of CAIX and showed that 42.7% of C33a-CAIX-wt and 50.9% of C33a-CAIX-A459G transfectants expressed CAIX protein. C33a cells transfected with mock control plasmid were used as a negative control. The data are presented as the mean, n = 2. ( c ) Effect of Ala459 mutation on CAIX-mediated extracellular acidification. The graph shows the differences between pHe values (ΔpH) of culture media from CAIX wt or A459G-transfected and mock-transfected cells cultured 48 h in hypoxia. A459G mutant reduced acidification of extracellular pHe when compared to control wild type C33a-CAIX transfectants. The data are presented as the mean ± s.d., n = 5. Statistical significance was analyzed using the Student’s t -test and expressed as a p -value (* p < 0.05). ( d ) Effect of Ala459 mutation on migration capacity of C33a cells. The graph depicts the results of the wound healing assay given as a % of the area covered by cells migrating to close the wound at 30 h after the scratch, measured at various positions along the wounds. Area covered by C33a cells expressing CAIX-wt was set as 100%. C33a cells expressing CAIX with mutated Ala459 exhibited slower migration. The data are presented as the mean ± s.d., n = 10. Statistical significance was analyzed using the Student’s t -test and expressed as a p -value (* p < 0.05). ( e ) Accumulation of the fluorescent sulfonamide (FITC-CA-i) occurred in hypoxic MDCK cells expressing the CAIX-wt, whereas it was diminished in hypoxic MDCK cell transfected with the CAIX-A459G mutant. Images were taken using objective 10×. ( f ) In situ detection of the interaction between CAIX and AE2 using a proximity ligation assay (PLA). Analysis was performed in C33a cells transiently transfected with CAIX-wt and A459G mutant and cultured in hypoxia for an additional 48 h. Red PLA signal indicates the existence of interaction or close proximity localization also between CAIX with mutated Ala459 and AE2. C33a-mock transfectants served as a negative assay control due to a lack of one target protein. CAIX protein was post-labelled in green, nuclei are blue. Images were taken using objective 40× and zoom 3.

Article Snippet: After 48 h of hypoxic incubation, transiently transfected cells were scraped into culture medium, centrifuged at low speed, washed twice with Versene solution and incubated with the CAIX-specific mouse monoclonal M75 antibody (1 µg/mL, BMC SAS, Bratislava, Slovakia) for 30 min at 4 °C.

Techniques: Western Blot, Transfection, Mutagenesis, Cell Culture, Fluorescence, Staining, Flow Cytometry, Plasmid Preparation, Negative Control, Migration, Wound Healing Assay, Expressing, In Situ, Proximity Ligation Assay