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during mouse colonocyte hyperproliferation
1 Department of Integrative Biology, Pharmacology, and Physiology, and 2 Department of Internal Medicine, Division of Gastroenterology, Hepatology, and Nutrition, University of Texas Health Science Center at Houston, Medical School, Houston, Texas 77030
Protein kinase (PK) C-
is implicated in the control of colonic epithelial cell proliferation
in vitro. However, less is known about its physiological role in vivo.
Using the transmissible murine colonic hyperplasia (TMCH) model, we
determined its expression, subcellular localization, and kinase
activity during native crypt hyperproliferation. Enhanced mitosis was
associated with increased cellular 72-kDa holoenzyme (PKC-
,
3.2-fold), 48-kDa catalytic subunit (PKM-
, 3- to 9-fold), and 24-kDa
membrane-bound fragment (Mf-
, >10-fold)
expression. Both PKC-
and PKM-
exhibited intrinsic kinase
activity, and substrate phosphorylation increased 4.5-fold. No change
in cellular PKC-
/PKM-
expression occurred. The subcellular distribution of immunoreactive PKC-
changed significantly: neck cells lost their basal subcellular pole filamentous staining, whereas
proliferating cell nuclear antigen-positive cells exhibited elevated
cytoplasmic, lateral membrane, and nuclear staining. Subcellular
fractionation revealed increased PKC-
and PKM-
expression and
activity within nuclei, which preferentially accumulated PKM-
. These
results suggest separate cellular and nuclear roles, respectively, for
PKC-
in quiescent and mitotically active colonocytes. PKM-
may
specifically act as a modulator of proliferation during TMCH.
protein kinase C; cellular mitosis; mouse colon
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