Fragmentation of Protein Kinase N (PKN) in the Hydrocephalic Rat Brain

Abstract

AHC PKN (protein kinase N; also called protein kinase C-related kinase (PRK-1)), is a serine/threonine protein kinase that is ubiquitously expressed in several organs, including the brain. PKN has a molecular mass of 120 kDa and has two domains, a regulatory and a catalytic domain, in its amino-terminals and carboxyl-terminus, respectively. Although the role of PKN has not been fully elucidated, previous studies have revealed that PKN is cleaved to a constitutively active catalytic fragment of 55 kDa in response to apoptotic signals. Hydrocephalus is a pathological condition caused by insufficient cerebrospinal fluid (CSF) circulation and subsequent excess of CSF in the brain. In this study, in order to elucidate the role of PKN in the pathophysiology of hydrocephalus, we examined PKN fragmentation in hydrocephalic model rats. Hydrocephalus was induced in rats by injecting kaolin into the cisterna magna. Kaolininduced rats (n=60) were divided into three groups according to the observation period after treatment (group 1: 3-6 weeks, group 2: 7-12 weeks, and group 3: 13-18 weeks). Shamtreated control rats, injected with sterile saline (n=20), were similarly divided into three groups. Spatial learning ability was estimated by a modified water maze test. Thereafter, brains were cut into slices and ventricular dilatation was estimated. Fragmentation of PKN was observed by Western blotting in samples collected from the parietal cortex, striatum, septal nucleus, hippocampus, and periaqueductal gray matter. All kaolin-induced rats showed ventricular dilatation. Most of them showed less spatial learning ability than those of sham-treated controls. In most regions, fragmentation of PKN had occurred in a biphasic manner more frequently than that in controls. The appearance of PKN fragmentation in periaqueductal gray matter was correlated with the extent of ventricular dilation and spatial learning disability. These results revealed that PKN fragmentation was observed in rats with kaolin-induced hydrocephalus, models for chronically-damaged brain dysfunction, suggesting that persistent brain insult, such as apoptosis, had occurred in these models. PKN fragmentation could be a hallmark for evaluating morphological and functional damage of the hydrocephalus.

PKN3 is the major regulator of angiogenesis and tumor metastasis in mice

“…One possible explanation would be that other PKN isoforms could compensate for the loss of PKN3 function in the context of tumor. PKN1, in particular, might be stimulated in the stromal cells inside of a tumor, because ischemic/hypoxic stress, which frequently happens inside of a tumor, is reported to activate or enhance the expression of PKN1 57 58 59 60 .…”

Protein kinase N1 critically regulates cerebellar development and long-term function

“…Activation of PKN1 is also achieved by caspase-3–mediated cleavage, resulting in a constitutively active protein product missing the regulatory N-terminus ( 9 ). This form of deregulated PKN1 activation occurs during apoptosis ( 10 ) and has been linked to various insults to the brain ( 11 – 14 ). We have previously reported that PKN1 is part of a purine-nucleoside signaling cascade involved in the protection of hypoxic neuronal cultures and cell lines in vitro ( 15 , 16 ).…”

Noradrenergic Pathways Involved in Micturition in an Animal Model of Hydrocephalus—Implications for Urinary Dysfunction

“…Following the surgery, all animals were monitored daily to evaluate body weight, head circumference, gait, and general appearance for any signs of hydrocephalus development. Like human patients, rats with kaolin-induced hydrocephalus present gait disturbances [2,26,27]. A set of reflexes and motor tests were conducted to evaluate the motor function of the animals.…”