Intracellular distribution pattern of procalcitonin in human monocytes and HepG2 cells

Introduction

Procalcitonin (PCT), the precursor of calcitonin, was recently forwarded as a diagnostic marker of systemic bacterial infection and sepsis. Previously we have demonstrated that PCT is expressed in human peripheral blood mononuclear cells (PBMC). Preliminary experiments indicated a PCT expression in HepG2 cells, too. Because of several homologies with cytoskeletal elements of PCT amino acids sequence we investigated the basal expression and distribution pattern of PCT in human monocytes and HepG2 hepatoma cells.

Methods

PBMC were prepared from heparinized venous blood samples from healthy volunteers by density gradient centrifugation. Monocytes were obtained by differential adhesion to plastic surface and cultivated up to 24 h. HepG2 human hepatoma cells were incubated under standard conditions. For the experiments cell lysates were used or cellular proteins were divided in cytoplasmatic, microtubular, nuclear-microfilamentous, and resulting pellet fraction. These protein fractions were analyzed by Western blot using monoclonal anti-calcitonin or anti-katakalcin (Lumitest^®, B.R.A.H.M.S, Berlin) or polyclonal anti-human calcitonin (Natutec, Frankfurt/M.) antibodies. For secondary immunofluorescence cells were fixed and incubated with the same antibodies used in western blotting.

Results

As verified by Western blotting and secondary immunofluorescence human monocytes and HepG2 hepatoma cells express PCT in association with cytoskeleton. The content of PCT seems to be higher in monocytes than in HepG2 cells. No PCT was found in cytoplasmic fraction.

Conclusion

We demonstrated for the first time an association of PCT with cytoskeletal components. Because of the high content of PCT in human monocytes it could be speculated that PCT has some intracellular physiological function outside systemic inflammation that have not been yet determined.