Exon 4 Encoded Sequence is a Major Determinant of Cytotoxicity of Apolipoprotein L1.

American journal of physiology. Cell physiology

PubMedID: 25924622

Khatua AK, Cheatham AM, Kruzel ED, Singhal PC, Skorecki K, Popik W. Exon 4 Encoded Sequence is a Major Determinant of Cytotoxicity of Apolipoprotein L1. Am J Physiol, Cell Physiol. 2015;ajpcell.00384.2014.
The APOL1 gene product is toxic to kidney cells, and its G1 and G2 alleles are strongly associated with increased risk for kidney disease progression in African Americans. Variable penetrance of the G1 and G2 risk alleles highlights the significance of additional factors which trigger or modify the progression of disease. In this regard, the effect of alternative splicing in the absence or presence of G1 or G2 alleles is unknown. In this study, we investigated whether alternative splicing of non-G1, non-G2 APOL1 (APOL1 G0) affects its biological activity. Out of seven APOL1 exons, exons 2 and 4 are differentially expressed in major transcripts. We found that in contrast to APOL1 splice variants B3 or C, variants A and B1 demonstrated strong toxicity in HEK293T cells. Subsequently, we established that exon 4 is a major determinant of toxicity of variants A and B1 and that extracellular release of these variants is dispensable for their cytotoxicity. Although only variants A and B1 induced nuclear translocation of TFEB, a master regulator of lysosomal biogenesis and autophagy, both exon 4-positive and -negative APOL1 variants stimulated perinuclear accumulation of unprocessed autophagosomes. Knockdown of endogenous TFEB did not attenuate APOL1 cytotoxicity, indicating that nuclear translocation of TFEB is dispensable for APOL1 toxicity. Our findings that a human podocyte cell line expresses both exon 4-positive and -negative APOL1 transcripts suggest that these variants may play a differential role in podocyte pathology. In summary, we have identified exon 4 as a major determinant of APOL1 G0 cytotoxicity.