[Expression and localization of endogenous C-reactive protein in THP-1 monocytes and LO2 hepatocytes]

To observe the expression and localization of endogenous C-reactive protein (CRP) in cells from different tissues under different conditions.

Macrophages differentiated from THP-1 monocytes with phorbol ester (PMA) induction and human LO2 hepatocytes were stimulated with lipopolysaccharide (LPS). The culture supernatant of the LPS-stimulated THP-1 cells was collected and added into LO2 cell culture, and after incubation, the cells were lysed to extract the proteins for SDS-PAGE and Western blotting. The stimulated cells were also examined immunocytochemically for CRP expression.

Western blotting detected CRP in both of the unstimulated cell lysates, but in neither of the two cell supernatants. After LPS stimulation, CRP expression was significantly increased in the cell lysate of THP-1 cells with also a small amount present in the supernatant, but CRP expression and release in the LO2 cells showed no significant variation. Treatment of the LO2 cells with the culture supernatant of LPS-stimulated THP-1 cells resulted in positivity of CRP in the cell lysate and the culture supernatant. Immunocytochemistry identified CRP expression throughout the THP-1 cell body (most obvious in the nuclei), which increased after LPS stimulation. In LO2 hepatocytes, CRP expression was found only outside the nuclei and increased after stimulation with the culture supernatant of LPS-treated THP-1 cells, especially obvious around the membrane.

CRP can not be up-regulated directly by LPS treatment in LO2 cells, but can be induced by certain cytokines (IL-6) secreted from LPS-stimulated THP-1 cells. The localization of CRP represents the characteristics of secreted protein in LO2 cells, but in THP-1 cells, CRP is found mainly in the cell nuclei.