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

Vitamin D3 is an essential vitamin that has been extensively studied due to its potential role as therapeutic for many diseases, including breast cancer. Previous research has indicated that calcitriol, the active form of Vitamin D3 has a negative effect on the metastatic ability of Inflammatory Breast Cancer (IBC) cells however the mechanism is not fully understood. The effect of calcitriol on IBC cells starting from cellular uptake must be investigated in order to understand these therapeutic effects. Calcitriol bound Quantum Dots (CalQDs) are a novel nanoparticle conjugated probe that can be used to directly examine the distribution, uptake, and signaling of calcitriol in live cells. Therefore we used these conjugated probes to directly investigate the uptake of calcitriol into live IBC cells. Interestingly, calcitriol uptake was observed to decrease when caveolae mediated endocytosis is disrupted. A luciferase assay confirmed that caveolae function is necessary; since calcitriol mediated activity decreases when caveolae mediated endocytosis is disrupted in IBC cells. In vitro examination of the localization of the probe indicated colocalization between caveolae and CalQDs. Additionally, Vitamin D Receptor (VDR) colocalization was observed with caveolae and calcitriol. This study demonstrates that in IBC cells calcitriol enters cells via caveolae mediated endocytosis and that caveolae are required for calcitriol to be uptaken at the increased rate.

Design of 1,25 dihydroxyvitamin D3 coupled quantum dots, a novel imaging tool.

1,25 dihydroxyvitamin D3 (Calcitriol), one of the active forms of Vitamin D, plays a vital role not only in calcium absorption but also during neuromuscular function and regulation of inflammation. Epidemiological studies suggest a preventive effect of Calcitriol in breast, colon and prostate cancer, however high concentrations of Calcitriol are necessary. Therefore targeted biologically active probes must be designed to determine Calcitriol distribution and dynamics in vitro and in vivo. Our Calcitriol probe remained stable over 2 days at 37 degrees C. When added to live C2C12 cells, the Calcitriol probe can be seen entering the nucleus within 2 hours and the probe activated the expression of the Vitamin D Response Element (VDRE), one of the major transcription elements. The Calcitriol probe provides a novel imaging tool that can be used to view Calcitriol localization and dynamics.