New insights into procathepsin D in pathological and physiological conditions

Procathepsin D is a major glycoprotein that is secreted from numerous types of cancer cells including breast, lung and prostrate carcinomas. It affects multiple stages of tumorigenesis that include proliferation, invasion, metastasis and apoptosis. Previous studies showed that the mitogenic effect of procathepsin D on cancer cells was mediated through its propeptide or activation peptide. Recent studies have also implicated the possible use of procathepsin D/activation peptide as a marker of cancer progression. Considering the broad range of functions of procathepsin D, the present review summarizes the three major potentials of procathepsin D-cancer progression, tumor marker and wound healing

Procathepsin D and cancer: From molecular biology to clinical applications

Procathepsin D (pCD) is overexpressed and secreted by cells of various tumor types including breast and lung carcinomas. pCD affects multiple features of tumor cells including proliferation, invasion, metastases and apoptosis. Several laboratories have previously shown that the mitogenic effect of pCD on cancer cells is mediated via its propeptide part (APpCD). However, the exact mechanism of how pCD affects cancer cells has not been identified. Recent observations have also revealed the possible use of pCD/APpcD as a marker of cancer progression. The purpose of this review is to summarize the three major potentials of pCD-tumor marker, potential drug, and screening agent

Inhibition of GADD34, the stress-inducible regulatory subunit of the endoplasmic reticulum stress response, does not enhance functional recovery after spinal cord injury.

Activation of the endoplasmic reticulum stress response (ERSR) is a hallmark of various pathological diseases and/or traumatic injuries. Restoration of ER homeostasis can contribute to improvement in the functional outcome of these diseases. Using genetic and pharmacological inhibition of the PERK-CHOP arm of the ERSR, we recently demonstrated improvements in hindlimb locomotion after spinal cord injury (SCI) and implicated oligodendrocyte survival as a potential mechanism. Here, we investigated the contribution of stress-inducible PPP1R15A/GADD34, an ERSR signaling effector downstream of CHOP that dephosphorylates eIF2α, in the pathogenesis of SCI. We show that although genetic ablation of GADD34 protects oligodendrocyte precursor cells (OPCs) against ER stress-mediated cell death in vitro and results in differential ERSR attenuation in vivo after SCI, there is no improvement in hindlimb locomotor function. Guanabenz, a FDA approved antihypertensive drug, was recently shown to reduce the burden of misfolded proteins in the ER by directly targeting GADD34. Guanabenz protected OPCs from ER stress-mediated cell death in vitro and attenuated the ERSR in vivo after SCI. However, guanabenz administration failed to rescue the locomotor deficits after SCI. These data suggest that deletion of GADD34 alone is not sufficient to improve functional recovery after SCI

The Proteostasis Network: A Global Therapeutic Target for Neuroprotection after Spinal Cord Injury

Proteostasis (protein homeostasis) is critical for cellular as well as organismal survival. It is strictly regulated by multiple conserved pathways including the ubiquitin-proteasome system, autophagy, the heat shock response, the integrated stress response, and the unfolded protein response. These overlapping proteostasis maintenance modules respond to various forms of cellular stress as well as organismal injury. While proteostasis restoration and ultimately organism survival is the main evolutionary driver of such a regulation, unresolved disruption of proteostasis may engage pro-apoptotic mediators of those pathways to eliminate defective cells. In this review, we discuss proteostasis contributions to the pathogenesis of traumatic spinal cord injury (SCI). Most published reports focused on the role of proteostasis networks in acute/sub-acute tissue damage post-SCI. Those reports reveal a complex picture with cell type- and/or proteostasis mediator-specific effects on loss of neurons and/or glia that often translate into the corresponding modulation of functional recovery. Effects of proteostasis networks on such phenomena as neuro-repair, post-injury plasticity, as well as systemic manifestations of SCI including dysregulation of the immune system, metabolism or cardiovascular function are currently understudied. However, as potential interventions that target the proteostasis networks are expected to impact many cell types across multiple organ systems that are compromised after SCI, such therapies could produce beneficial effects across the wide spectrum of highly variable human SCI

GADD34^-/- mOPCS show enhanced survival in response to ER stress.

<p>(A) Quantification using MTT assay show increased survival of GADD34^-/- mOPCs exposed to tunicamycin (Tm; 0.01 µg/ml) at only 24 hours. (B,C) Western blot shows sustained translational repression in GADD34^-/- mOPCs in contrast to WT mOPCs. (D) RT-PCR data shows attenuation in the ERSR in GADD34^-/- mOPCs exposed to Tm for 16 hours. Data (A,C,D) are the mean ± SD (n = 4, ** p<0.01).</p

<i>In vivo</i> administration of guanabenz results in increased phosphorylation of eIF2α and modulates the key ERSR markers 6 hours post-SCI.

<p>(A) Schematic representation of guanabenz injections given at various time points-post SCI. (B,C) Western blots show that guanabenz significantly increases phosphorylated eIF2α levels at the injury epicenter of contused spinal cords. (D) Guanabenz leads to differential modulation in ERSR transcript levels as analyzed by qRT-PCR. Transcript levels are expressed as fold changes compared with respective levels in sham controls. Data are the mean ± SD [n = 3 (B,C); n = 4 (D), * p<0.05, **p<0.01].</p

Deletion of GADD34 results in attenuation of the ERSR after SCI.

<p>Total RNA was extracted from injury epicenter of WT and GADD34^-/- mice at (A) 6 hours and (B) 24 hours-post SCI. Transcript level (normalized to GAPDH) is expressed as fold changes compared with levels in sham controls. Data (A,B) are the mean ± SD (n = 4, ** p<0.01).</p

Locomotor assessment in GADD34^-/- mice after SCI.

<p>(A) BMS locomotor analyses performed weekly following moderate SCI did not reveal any functional recovery in GADD34^-/- mice (solid squares) compared to WT mice (solid diamonds). Analysis of BMS subscore post-SCI showed no significant differences in stepping characteristics between the two groups (inset). There is no significant difference in the neuron- (B), astrocyte-(C) and oligodendrocyte-specific (D) transcript levels as indicated between WT and GADD34^-/- mice 72 hours post-SCI. Data (A,B) are the mean ± SD (n = 9).</p

Administration of guanabenz does not enhance hindlimb locomotor function after SCI.

<p>(A) Open field BMS locomotor analyses performed weekly did not reveal any significant differences between vehicle- and guanabenz-treated animals. Analysis of BMS subscore also did not show any differences in stepping characteristics between the two groups (inset). Guanabenz treatment does not result in significant differences in the neuron- (B), astrocyte-(C) and oligodendrocyte-specific (D) transcript levels (as indicated) compared to vehicle-treated mice at 72 hours post-SCI. Data (A,B) are the mean ± SD (n = 6).</p