Identification of Z11 as a novel zinc finger protein in the lungs

Abstract

Proteomic analysis of nuclear proteins isolated from murine lungs led to the identification of an uncharacterized zinc finger protein (Z11). We sought to identify the role Z11 plays in normal cell physiology and during infection. Examination of the amino acid sequence revealed that Z11 belongs to the DNA polymerase β-like nucleotidyltransferase superfamily, contains four zinc finger-like motifs, poly A polymerase catalytic and associated domains, and is highly conserved among vertebrates. We find that Z11 mRNA is expressed in multiple tissues at approximately equivalent levels when normalized to 18S rRNA via real-time RT-PCR. Unlike the transcript levels, the amount of Z11 protein was variable in the different murine tissues examined. Z11 protein levels are highest in the spleen and lungs and are undetectable in bone marrow, kidney, liver, or skeletal muscle. Interestingly, the nuclear content of Z11 was decreased 24 to 48 hours after mice were intratracheally infected with Escherichia coli. In contrast to the variable expression among murine tissues, Z11 protein is detected in all of 8 different cell lines examined. The overexpression of Z11 is toxic to most cell lines, but tolerated by Chinese hamster ovary (CHO) and human embryonic kidney (HEK 293) cells. In contrast to the cellular toxicity observed during Z11 overexpression, targeted knock-down of Z11 caused no defect in viability. Based on Z11 sequence homology and conserved domain motifs, Z11 is potentially involved in RNA turnover or posttranscriptional modifications. To this end, our current and future studies aim to identify the physiologic roles Z11 plays in modifying RNA in murine lungs and its biologic impact during pneumonia.