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Ординатура / Офтальмология / Английские материалы / Retinal Degenerative Diseases Laboratory and Therapeutic Investigations_Anderson_2008.pdf
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86

D.B. Farber et al.

trypsin-digested and subjected to MALDI-TOF-MS spectrometry. SAFB1 (scaffold attachment factor B1) is one of the proteins that were identified by mass spectrometry analysis. We are currently determining whether it interacts with ZBED4 (Table 10.1).

Table 10.1 Putative proteins interacting with ZBED4

Protein

Mr(expt)

Mr(calc)

Score

Peptide

 

 

 

 

 

SAFB1

1160.3943

1160.6111

69

K.ILDILGETCK.S

SF3B2

1231.3069

1231.6237

47

R.YGPPPSYPNLK.I

HNRPU

1646.9186

1646.8376

74

R.NFILDQTNVSAAAQR.R

 

 

 

 

 

10.3 Discussion

In the present study, we analyzed the expression of the novel ZBED4 mRNA and its encoded protein in human and mouse retinas, and in transfected HEK 293 cells. ZBED4 is an 1171 amino acid ( 135 kDa) protein that has all the typical features of a nuclear regulatory protein. It contains four zinc finger BED domains with the characteristic Cx2CxnHx3–5[H/C] signature in the amino-terminal-half, and a hATC dimerization domain in the carboxy-terminal end. In addition, two nuclear receptorinteracting modules (LXXLL) are present in the ZBED4 amino acid sequence.

Our in situ hybridization and FACS results indicated that the ZBED4 mRNA is expressed mostly in cone cells. Immunocytochemical localization of ZBED4 in human retinal sections using anti-ZBED4 antibodies showed a positive reaction in the inner segments of photoreceptors that were PNA-labeled, also indicating that the ZBED4 protein is expressed predominantly in cones. In addition, we demonstrated that the expression of this protein in the human retina is not only neuronal but, to a lesser degree, also glial, since we found it in the endfeet of Müller cells.

MALDI-TOF-MS spectrometry analysis of the ZBED4 protein band from the lane of the SDS-gel containing the enriched ZBED4 also identified another protein in the same band: the scaffold attachment factor B1. SAFB1 is known to be involved in chromatin organization, transcriptional regulation, RNA metabolism, stress response and can also function as a potent ERα co-repressor (Townson et al. 2003). Over-expression of SAFB1 inhibits ERα-mediated transcription, while its deletion from mouse embryo fibroblasts results in increased ERα activity (Oesterreich 2003). Since the sequence of ZBED4, just as that of SAFB1, indicates the presence of two nuclear receptor-interacting modules (LXXLL), ZBED4 may also be a co-activator/co-repressor of nuclear hormone receptors (NHRs). Therefore, we decided to characterize the interaction of ZBED4 and SAFB1 and to determine if they are part of the same activating or repressing complex. In addition to mediating effects of NHRs, some co-activators/co-repressors also seem to enhance the activity of other transcription factors such as c-Fos and c-Jun while others do not bind directly to NHRs but markedly enhance their ligand-dependent transcriptional

10 ZBED4, A Novel Retinal Protein Expressed in Cones and Müller Cells

87

activity in vivo by modulating another co-activator’s activity (Clark et al. 1995). The characterization of ZBED4 and SAFB1 interaction will determine whether the complex binds to ERα and stimulates the transcription of cone-specific genes that have ERα response elements in their promoters. These studies may be of great significance as several epidemiological investigations have shown that changes in gene expression resulting from variations in hormonal regulation are associated with the incidence of ocular conditions such age-related macular degeneration (AMD) and idiopathic full thickness macular hole.

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