1,25 Dihydroxyvitamin D3 uptake is localized at caveolae and requires caveolar function

Area of Science:

• Oncology
• Cell Biology
• Nanotechnology

Background:

• Vitamin D3 (calcitriol) shows therapeutic potential for breast cancer, particularly inflammatory breast cancer (IBC).
• The precise mechanism by which calcitriol affects IBC cells, including its cellular uptake, remains incompletely understood.
• Investigating calcitriol uptake is crucial for elucidating its therapeutic effects in IBC.

Purpose of the Study:

• To investigate the cellular uptake mechanism of calcitriol in live IBC cells.
• To determine the role of specific endocytic pathways in calcitriol uptake.
• To explore the relationship between calcitriol, its receptor, and cellular uptake mechanisms.

Main Methods:

• Utilized novel Calcitriol bound Quantum Dots (CalQDs) for real-time tracking of calcitriol in live IBC cells.
• Investigated calcitriol uptake under conditions where caveolae-mediated endocytosis was disrupted.
• Employed a luciferase assay to assess calcitriol-mediated activity.
• Performed in vitro colocalization studies using CalQDs, caveolae markers, and the Vitamin D Receptor (VDR).

Main Results:

• Calcitriol uptake into IBC cells significantly decreased when caveolae-mediated endocytosis was inhibited.
• Disruption of caveolae function led to a reduction in calcitriol-mediated activity, confirmed by luciferase assay.
• In vitro studies showed colocalization of CalQDs with caveolae, indicating calcitriol enters cells via this pathway.
• Colocalization of the Vitamin D Receptor (VDR) with both caveolae and calcitriol was observed.

Conclusions:

• Calcitriol is internalized by inflammatory breast cancer cells through caveolae-mediated endocytosis.
• Caveolae are essential for the efficient uptake of calcitriol in IBC cells.
• This study elucidates a key cellular mechanism for calcitriol action in breast cancer, paving the way for targeted therapies.