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David Wan-Cheng Li, Hua Xiang, Uwe Fass, Xin-Yuan Zhang; Analysis of Expression Patterns of Protein Phosphatase-1 and Phosphatase-2A in Rat and Bovine Lenses. Invest. Ophthalmol. Vis. Sci. 2001;42(11):2603-2609.
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purpose. The reversible phosphorylation and dephosphorylation at the serine and
threonine residues on proteins play distinct roles in regulating
multiple cellular activities. Whereas the protein serine-threonine
kinases have been well studied in the lens system, very little is known
about the expression and function of the serine-threonine phosphatases.
The present article reports the expression patterns of protein
phosphatase (PP)-1 and -2A in adult rat and bovine lenses.
methods. Total RNAs and proteins were extracted from the epithelial and fiber
cells of rat and bovine lenses. RT-PCR and Northern blot analysis were
used to detect the mRNA expression levels in the epithelial cells and
different fractions of fiber cells of these two types of lenses.
Western blot was used to examine the protein expression levels in these
different samples. An enzymatic assay was used to detect the activity
distribution of PP-1 and -2A in these samples.
results. The mRNAs for the PP-1 catalytic subunit (PP-1cs) and PP-2A catalytic
subunit (PP-2Acs) were expressed in both epithelial and fiber cells of
rat and bovine lenses. A detailed examination of the expression
patterns of the two mRNAs in different fractions of fiber cells
revealed that the cortical fiber cells (F1) contain the highest level
of PP-1cs and -2Acs mRNAs (similar to those in the epithelial cells)
among different fractions of fiber cells. The levels of the two mRNAs
were sequentially decreased in the next layers of fiber cells (F2 and
F3) and became barely detectable in the inner layers of fiber cells (F4
and N). In contrast to the mRNA expression patterns, the PP-1cs protein
was mainly found in the epithelial cells. Among different layers of
fiber cells, only cortical (F1) fiber cells contained detectable level
of PP-1cs protein (bovine lenses contained a relatively higher level of
PP-1cs than rat lenses in this region). In the remaining fiber cells,
the PP-1cs protein was hardly detectable in rat lenses and slightly
detectable in bovine lenses. The PP-2Acs protein was detectable only in
the lens epithelial cells. Enzymatic assays revealed that the
distribution patterns of PP-1 and -2A activities were similar to those
of PP-1cs and -2Acs proteins. Furthermore, PP-1 activity was
approximately four to five times higher than PP-2A activity in the lens
conclusions. This study demonstrates that active PP-1 and -2A are mainly distributed
in the lens epithelial cells, with PP-1 as a major phosphatase. The
mRNAs and proteins for PP-1cs and -2Acs are differentially expressed in
the epithelial and fiber cells of rat and bovine
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