Effects of heat shock on the distribution and expression levels of nuclear proteins in HeLa S3 cells

Abstract

Cumulating evidence has led to the idea that nuclear functions such as DNA replication, RNA transcription, RNA splicing and nucleocytoplasmic transport are facilitated by a proteinaceous architectural framework within the nuclear compartment and at the nuclear envelope. In the present study, we have used immunofluorescence microscopy and quantitative Western blotting to compare the distribution and expression levels of several nuclear proteins during the response of HeLa S3 cells to both mild and severe hyperthermia. Cells were exposed to mild (42 degrees C) or severe (45 degrees C) hyperthermia treatment for 90 min and left to recover at 37 degrees C for 1-25 h. The cell response was monitored immediately after the heat stress and at different time intervals during the recovery period. Our observations indicate that inner nuclear membrane proteins, LAP2beta and emerin, as well as major components of the nuclear lamina, lamins A/C and lamin B1, maintain an overall normal distribution at the nuclear periphery throughout the cell response to mild or severe hyperthermia. The response was nevertheless characterized by significant changes in the expression levels of emerin following recovery from a mild stress and of lamin B1 after recovery from a severe stress. Our results also provide evidence that the organization of functional domains within the nuclear interior such as nucleoli and splicing speckles differs between cells responding to a mild or a severe stress. Mild hyperthermia was accompanied by a significant decrease in the expression level of the nucleolar protein 2H12 whereas severe hyperthermia was characterized by a reduction in the expression of the nucleocytoplasmic shuttling protein 2A7. Our data underline the complexity of nuclear function/structure relationships and the needs for a better understanding of protein-protein interactions within the nuclear compartment.