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SOLUBILITY PARTITIONING OF C/EBPβ ON THE RAT HEPATOCYTE NUCLEAR MATRIX BY HYDROPHOBIC INTERACTIONS
Author(s) -
Uskoković Aleksandra,
Vidaković Melita,
Dinić Svetlana,
IvanovićMaticć Svetlana,
Martinović Vesna,
Poznanović Goran
Publication year - 2002
Publication title -
cell biology international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.932
H-Index - 77
eISSN - 1095-8355
pISSN - 1065-6995
DOI - 10.1006/cbir.2002.0888
Subject(s) - nuclear matrix , nuclear lamina , chemistry , nuclear protein , biochemistry , microbiology and biotechnology , chromatography , biology , transcription factor , dna , chromatin , gene
The greatest part of nuclear C/EBPβ (a major 35kD protein, 30 and 38kD isoforms) was observed to partition with the nuclear matrix. Cross‐linking experiments with formaldehyde suggested that the association reflected the in situ juxtapositioning of C/EBPβ to nuclear matrix proteins in isolated nuclei. The association of C/EBPβ with the nuclear matrix resisted RNase and DNase treatment and extraction with protein sulfhydryl reducing agents combined with high ionic strength salt. C/EBPβ displayed a proclivity to extensively reassemble with the filament‐forming nuclear matrix proteins after a cycle of solubilization with urea, followed by its removal by dialysis. These findings suggest that the C/EBPβ moieties were anchored to the nuclear matrix through hydrophobic protein‐protein interactions with the lamins. Subsequent separation of nuclear matrix‐associated C/EBPβ into insoluble, reassembling, and soluble nuclear matrix protein (SNMP) fractions after a cycle of solubilization/reassembly pointed to the sub‐partitioning of C/EBPβ on the nuclear matrix. DNA affinity chromatography using the rat haptoglobin gene cis ‐element and SNMP revealed the binding of p35 during basal transcription, and p35 and p30 during elevated haptoglobin gene transcription in the course of the acute‐phase (AP) response. It was concluded that the appearance of cis ‐element‐binding p30 in the SNMP fraction resulted from its increased solubility (decreased hydrophobicity) and inability to reassociate with the lamins during urea removal. The observed solubility partitioning of C/EBPβ on the nuclear matrix framework could represent a level of control of the general availability of regulatory proteins for establishing interactions with DNA.