PKD3 localizes to late endosomes to maintain Rab7-dependent endolysosomal homeostasis

Area of Science:

• Oncology
• Cell Biology
• Molecular Biology

Background:

• Protein kinase D3 (PKD3) is implicated in triple-negative breast cancer (TNBC) progression, driving invasion, proliferation, and stemness.
• The precise mechanisms by which PKD3 exerts these effects remain largely unelucidated.

Purpose of the Study:

• To investigate the role of PKD3 in regulating cellular functions within TNBC.
• To elucidate the molecular mechanisms underlying PKD3's contribution to TNBC progression and cancer stem cell maintenance.

Main Methods:

• Immunofluorescence microscopy to determine endogenous PKD3 localization in MDA-MB-231 cells.
• Analysis of Rab7-positive vesicle characteristics and retromer complex recruitment upon PKD3 depletion.
• Assessment of cathepsin D secretion and endosomal acidification.
• Evaluation of Wnt signaling pathway activity and cancer stem cell markers.

Main Results:

• Endogenous PKD3 localizes to Rab7-positive vesicles in TNBC cells cultured on stiff matrices.
• PKD3 depletion leads to smaller Rab7-positive vesicles, reduced retromer recruitment, and increased cathepsin D secretion.
• Impaired endosomal acidification was observed in PKD3-depleted cells, correlating with Wnt signaling dysregulation and reduced stemness.

Conclusions:

• PKD3 plays a novel role in regulating endolysosomal trafficking and dynamics within TNBC cells.
• PKD3-mediated regulation of endolysosomal acidification is crucial for maintaining the cancer stem cell population in TNBC.
• Targeting PKD3 may offer a therapeutic strategy for disrupting TNBC stemness and progression.