Department of Cellular Biology and Anatomy, Medical College of Georgia at Augusta University, Augusta, Georgia, United States.
Geisinger Commonwealth School of Medicine, Scranton, Pennsylvania, United States.
Am J Physiol Cell Physiol. 2024 Oct 1;327(4):C1094-C1110. doi: 10.1152/ajpcell.00564.2023. Epub 2024 Sep 9.
The class 3 phosphatidylinositol 3-kinase (Pik3c3) plays critical roles in regulating autophagy, endocytosis, and nutrient sensing, but its expression profile in the kidney remains undefined. Recently, we validated a Pik3c3 antibody through immunofluorescence staining of kidney tissues from cell type-specific Pik3c3 knockout mice. Immunohistochemistry unveiled significant disparities in Pik3c3 expression levels across various kidney cell types. Notably, renal interstitial cells exhibit minimal Pik3c3 expression. Further, coimmunofluorescence staining, utilizing nephron segment- or cell type-specific markers, revealed nearly undetectable levels of Pik3c3 expression in glomerular mesangial cells and endothelial cells. Intriguingly, although podocytes exhibit the highest Pik3c3 expression levels among all kidney cell types, the renal proximal tubule cells (RPTCs) express the highest level of Pik3c3 among all renal tubules. RPTCs are known to express the highest level of the epidermal growth factor receptor (EGFR) in adult kidneys; however, the role of Pik3c3 in EGFR signaling within RPTCs remains unexplored. Therefore, we conducted additional cell culture studies. The results demonstrated that Pik3c3 inhibition significantly delayed EGF-stimulated EGFR degradation and the termination of EGFR signaling in RPTCs. Mechanistically, Pik3c3 inhibition surprisingly did not affect the initial endocytosis process but instead impeded the lysosomal degradation of EGFR. In summary, this study defines, for the first time, the expression profile of Pik3c3 in the mouse kidney and also highlights a pivotal role of Pik3c3 in the proximal tubule cells. These findings shed light on the intricate mechanisms underlying Pik3c3-mediated regulation of EGFR signaling, providing valuable insights into the role of Pik3c3 in renal cell physiology. This is the first report defining the class 3 phosphatidylinositol 3-kinase (Pik3c3) expression profile in the kidney. Pik3c3 is nearly absent in renal interstitial cells, glomerular mesangial cells, and endothelial cells. Remarkably, glomerular podocytes express the highest Pik3c3 level in the kidney. However, the proximal tubule exhibits the highest expression level among all renal tubules. This study also unveils the pivotal role of Pik3c3 in regulating EGFR degradation and signaling termination in RPTCs, furthering our understanding of Pik3c3 in renal cell physiology.
该 3 类磷脂酰肌醇 3-激酶（Pik3c3）在调节自噬、内吞作用和营养感应方面发挥着关键作用，但它在肾脏中的表达谱尚不清楚。最近，我们通过对细胞类型特异性 Pik3c3 敲除小鼠的肾脏组织进行免疫荧光染色验证了一种 Pik3c3 抗体。免疫组织化学揭示了各种肾脏细胞类型中 Pik3c3 表达水平的显著差异。值得注意的是，肾间质细胞表达的 Pik3c3 水平最低。此外，利用肾单位节段或细胞类型特异性标志物进行共免疫荧光染色，发现肾小球系膜细胞和内皮细胞中几乎检测不到 Pik3c3 的表达。有趣的是，尽管足细胞是所有肾脏细胞类型中 Pik3c3 表达水平最高的，但在所有肾单位中，近端肾小管细胞（RPTCs）表达的 Pik3c3 水平最高。众所周知，RPTCs 在成人肾脏中表达最高水平的表皮生长因子受体（EGFR）；然而，Pik3c3 在 RPTCs 中的 EGFR 信号中的作用仍未被探索。因此，我们进行了额外的细胞培养研究。结果表明，Pik3c3 抑制显著延迟了 EGF 刺激的 EGFR 降解和 EGFR 信号的终止。从机制上讲，Pik3c3 抑制并没有影响初始内吞过程，而是阻碍了 EGFR 的溶酶体降解。总之，这项研究首次定义了 Pik3c3 在小鼠肾脏中的表达谱，并强调了 Pik3c3 在近端肾小管细胞中的关键作用。这些发现揭示了 Pik3c3 介导的 EGFR 信号调节的复杂机制，为 Pik3c3 在肾脏细胞生理学中的作用提供了有价值的见解。这是首次报道定义肾脏中 3 类磷脂酰肌醇 3-激酶（Pik3c3）的表达谱。Pik3c3 在肾间质细胞、肾小球系膜细胞和内皮细胞中几乎不存在。值得注意的是，肾小球足细胞在肾脏中表达最高水平的 Pik3c3。然而，在所有肾单位中，近端肾小管的表达水平最高。这项研究还揭示了 Pik3c3 在调节 RPTCs 中 EGFR 降解和信号终止中的关键作用，进一步加深了我们对 Pik3c3 在肾脏细胞生理学中的理解。
