The PKC-specific activator, RACK (0.2 mg/kg), and the PKC-specific inhibitor, V1-1 (0.2 mg/kg) [4], were injected intraperitoneally at the onset of reperfusion. protection than either alone, indicating they likely act independently. Keywords:Cerebral ischemia, MEK/ERK cascade, PKC, ERK1/2 == 1. Introduction == The mitogen-activated protein kinase (MAPK) and the protein kinase C (PKC) pathways are implicated in neuronal death and survival after stroke [4,5,23]. The best characterized members in the MAPK pathways are extracellular signal-regulated kinase 1 and 2 (ERK1/2), whose activity is usually regulated by a three tiered kinase module, RafMEKERK, and is increased when ERK1/2 are phosphorylated [25]. ERK1/2 activity is usually reported to be involved in ischemic injury: levels of phosphorylated ERK1/2 (P-ERK1/2) increase after stroke [23]. But previous studies have shown that increases in P-ERK1/2 are associated GW4064 with both neuronal survival and death [16,23], and whether ERK1/2 activity exacerbates or attenuates ischemic injury is controversial [27]. The PKC family consists of 10 isozymes of serine/threonine kinases with distinct functions for neuronal survival [3]. For instance, PKC, one member of the PKC family, is usually pro-apoptotic [4]. We as well GW4064 as others have shown that PKC activity increases after stroke [32]; it is cleaved, and translocates to the particulate membrane after stroke [24,32]. In addition, the PKC-specific inhibitor peptide, V1-1, reduces ischemic injury by blocking PKC subcellular translocation [4] and the RACK, the PKC-selective activator, inhibits protection induced by lowering body temperature after stroke [32]. ERK1/2 interacts GW4064 with the PKC pathways in non-neuronal systems [1,9,13]. PKC directly activates the MAPK pathway by phosphorylating Raf, a signaling molecule which functions Prp2 upstream of ERK1/2 [6,17]. In addition, VEGF-induced ERK1/2 activation requires PKC activation and translocation [18], and PKC has positive feedback around the MAPK pathway [2]. Conversely, activation of ERK1/2 during apoptosis induced by DNA damage involves PKC [1]. Nevertheless, whether ERK1/2 interacts with PKC after stroke, and how such interplay affects ischemic injury has not been studied. In this study, we first examined whether inhibiting ERK1/2 by U0126, a MEK1/2 inhibitor, reduces infarct size after stroke, then clarified how the PKC inhibitor, V1-1, affects the levels of phosphorylated ERK1/2, and finally decided whether PKC and ERK1/2 signaling pathways interact in the response to stroke. == 2. Results == The effects of the ERK1/2 inhibitor (U0126), the PKC inhibitor (V1-1), and the PKC activator (RACK) around the levels of phosphorylated ERK1/2 (P-ERK1/2) were evaluated/decided. The results of Western blot analysis showed that P-ERK1/2 levels transiently increased from 1 to 4 h after reperfusion in the ischemic cortex (Fig. 1), which is usually consistent with previous reports [23]. As expected, the ERK1/2 inhibitor, U0126, injected at ischemia onset, attenuated increases in P-ERK1/2 levels at 4 h (Fig. 2). Interestingly, the PKC-selective inhibitor, V1-1, did not change P-ERK1/2 levels compared with the vehicle. In contrast, the PKC-selective activator, RACK, reduced ERK1/2 phosphorylation when measured 4 h after reperfusion (Fig. 2). Total levels of ERK did not change (data not shown). == Fig. 1. == P-ERK1/2 levels transiently increased in the ischemic penumbra after reperfusion. (A) Representative Western blot analysis with anti-P-ERK1/2 and anti-ERK1/2 of samples from the ischemic cortex (penumbra) at 0 min, 15 min, 1 h, 2 h, 4 h, 24 h and 48 h after reperfusion. -actin was used to normalize protein loading. (B) Bar graphs show relative optical densities of P-ERK1/2 bands normalized to that of the sham. Total ERK1/2 protein did not change after stroke (data not shown). *P< 0.05,vs. sham.n= 7 per group. == Fig. 2. == The effect of.