Figure 5. Re-expression of wild type FH in HLRCC tumor-derived cell lines did not restore a functional respiratory chain.

(A) In-gel assay of FH activity in five HLRCC FH^−/− cell lines and in the FH^−/− cell lines after re-expression of wild type HA-tagged FH. HRCE and RPTEC cells were used as controls. The presence of the HA tag resulted in a faster mobility of the recombinant FH tetramers (FH^WT-HA) on native gels compared to endogenous FH (FH^WT) in HRCE and RPTEC cells. (B) Immunoblots for FH and HA-tag in the same cell lines as in (A). The cytoplasmic protein malate dehydrogenase (MDH1) was used as a loading control for total protein. (C) In-gel NADH dehydrogenase assay to assess Complex I (CI) activity in the same cell lines as in (A). CI-CIII₂-CIV_n indicates supercomplexes containing Complex I, dimeric Complex III and one to four copies of Complex IV. (D) Mitochondrial lysates from the cell lines indicated in (A) were analyzed by native IB for the nuclear-encoded NDUFS1 to assess Complex I levels and assembly. (E) Mitochondrial lysates from the cell lines indicated in (A) were analyzed by native IB for the nuclear-encoded Complex III subunit UQCRC2 to assess Complex III levels. (F) In-gel cytochrome c oxidase activity for Complex IV activity was performed in the same cell lines as in (A). (G) Mitochondrial lysates from the cell lines indicated in (A) were analyzed by native IB for the mtDNA-encoded MT-CO1 to assess Complex IV assembly. (H) Mitochondrial lysates from the cell lines indicated in (A) were analyzed by native IB for the nuclear-encoded ATP5A to assess Complex V assembly. (I) Mitochondrial lysates from the cell lines indicated in (A) were analyzed by SDS IB for the Complex I subunit NDUFS1, Complex III subunit UQCRC2, Complex IV subunit MT-CO1 and Complex V subunit before and after restoration of FH expression. Data shown in (A) to (I) are representative of three independent experiments.