Conover, Cheryl A.

Wreaking havoc while (growth-)arrested Cells enter a state of senescence in response to certain stresses. Studying mouse models, Childs et al. examined the role of senescent lipid-loaded macrophages (so-called “foam cells”) in the pathogenesis of atherosclerosis. At early stages of atherosclerosis, senescent foam cells promoted the expression of inflammatory cytokines. At later stages, they promoted the expression of matrix metalloproteases implicated in the rupture of atherosclerotic plaque, which can lead to blood clots. Experimental removal of the senescent cells had beneficial effects at both stages of the disease. Science , this issue p. 472

Insulin-like growth factors (IGFs) are implicated in the development of diabetic nephropathy (DN) and are shown to increase proliferation and extracellular matrix production in mesangial cells. The IGF system is complex and is composed of ligands, receptors, six binding proteins (IGF BPs) and a novel zinc metalloproteinase – pregnancy-associated plasma protein (PAPP)-A. PAPP-A increases the local bioavailability of IGF through the cleavage of IGF BP-4. Mesangial expansion is a major component of DN, and PAPP-A is shown to be increased in the glomeruli of patients with DN. Therefore, we determined the expression of PAPP-A and components of the IGF system in normal human mesangial cells (HMCs) and their regulation by factors known to be involved in DN. Under basal conditions, HMCs expressed PAPP-A, IGF1 receptor and all six IGF BPs. Interleukin (IL)-1β was the most potent stimulus for PAPP-A expression (5-fold) followed by tumor necrosis factor (TNF)-α (2.5-fold). This PAPP-A was secreted, cell associated and proteolytically active. IL1β also increased IGF BP-1expression (3-fold) with either reduction or no effect on other IGF BPs. Generally, TNF-α treatment decreased IGF BP expression. No treatment effect on PAPP-A or IGF BPs was seen with IL6, IGFs, advanced glycation end products or prolonged hyperglycemia. In addition, stimulation of HMCs with IGF1 alone or IGF1 complexed to wild-type, but not protease-resistant, IGF BP-4 led to increased [ 3 H]-thymidine incorporation. In conclusion, these novel findings of PAPP-A and its regulation by proinflammatory cytokines, as well as the comprehensive analysis of the IGF system regulation in HMCs, suggest a mechanism by which inflammatory states such as DN can impact IGF activity in the kidney.

Abstract The majority of ovarian cancer patients acquire resistance to standard platinum chemotherapy and novel therapies to reduce tumor burden and ascites accumulation are needed. Pregnancy-associated plasma protein-A (PAPP-A) plays a key role in promoting insulin-like growth factor (IGF) pathway activity, which directly correlates to ovarian cancer cell transformation, growth, and invasiveness. Herein, we evaluate PAPP-A expression in tumors and ascites of women with ovarian cancer, and determine the antitumor efficacy of a neutralizing monoclonal PAPP-A antibody (mAb-PA) in ovarian cancer using primary patient ovarian tumorgrafts (“Ovatars”). PAPP-A mRNA expression in patient ovarian tumors correlated with poor outcome and was validated as a prognostic surrogate in Ovatar tumors. Following confirmation of mAb-PA bioavailability and target efficacy in vivo, the antitumor efficacy of mAb-PA in multiple Ovatar tumor models was examined and the response was found to depend on PAPP-A expression. Strikingly, the addition of mAb-PA to standard platinum chemotherapy effectively sensitized platinum-resistant Ovatar tumors. PAPP-A protein in ascites was also assessed in a large cohort of patients and very high levels were evident across the entire sample set. Therefore, we evaluated targeted PAPP-A inhibition as a novel approach to managing ovarian ascites, and found that mAb-PA inhibited the development, attenuated the progression, and induced the regression of Ovatar ascites. Together, these data indicate PAPP-A as a potential palliative and adjunct therapeutic target for women with ovarian cancer. Mol Cancer Ther; 14(4); 973–81. ©2015 AACR.

Pregnancy-associated plasma protein-A (PAPP-A) is a novel zinc metalloproteinase implicated in cardiovascular disease. The aim of this study was to determine whether a reduction in PAPP-A expression in the adult affects the progression of established atherosclerotic plaque. Apolipoprotein E-null mice were fed a high-fat diet for 5 weeks to initiate early-stage plaque development before tamoxifen-inducible, Cre recombinase–mediated excision of the floxed PAPP-A gene. High-fat feeding was continued, and after 10 weeks the aorta and brachiocephalic artery were harvested for atherosclerotic plaque analyses of overall burden and morphology, respectively. An inducible decrease in PAPP-A gene expression significantly inhibited atherosclerotic plaque progression as assessed by a 70% reduction in plaque burden in the aorta (P = .012) without an effect on the elevated circulating levels of cholesterol and triglycerides in this model. Furthermore, this reduction in PAPP-A prevented the development of advanced plaque with necrotic cores and buried fibrous caps in the brachiocephalic artery. These data indicate PAPP-A as a potential target to limit progression of established atherosclerotic plaque.

Hepatitis C-associated osteosclerosis (HCAO) is a rare syndrome of adult-onset osteosclerosis. An understanding of the factor(s) leading to the stimulation of bone formation in these patients may provide novel anabolic approaches for the treatment of osteoporosis. We have demonstrated that HCAO patients have a specific increase in circulating big IGF-II (IGF-IIE) and IGF-binding protein-2 (IGFBP-2) levels, and that IGF-IIE and IGFBP-2 circulate together in a bioavailable, 50-kDa complex. Patients with nonislet cell tumor hypoglycemia (NICTH) also have increased circulating IGF-IIE and IGFBP-2 levels. However, HCAO patients do not exhibit hypoglycemia, nor do NICTH patients exhibit obvious osteosclerosis. Thus, to better understand the reason(s) for the differing clinical manifestations of the IGF-IIE excess in the two syndromes, we characterized IGF-IIE in HCAO and NICTH sera using recently developed antibodies (Ab) recognizing either the full-length IGF-IIE 89-amino acid C-terminal extension peptide (IIE138–156 Ab) or specific cleavage forms of IGF-IIE (IIE78–88 Ab and IIE89–101 Ab). The predominant IGF-IIE form in HCAO serum migrated on SDS-PAGE as a single band at approximately 18 kDa that reacted with the IIE89–101 Ab. On the other hand, the predominant form in NICTH serum migrated as a doublet of 14 and 16 kDa that reacted with the IIE78–88 Ab. There results are consistent with differential processing of the IGF-IIE precursor at predicted cleavage sites producing IGF-IIE1–104 and IGF-IIE1–88 in HCAO and NICTH, respectively. As these two forms may have differing biological activities and/or targeting properties, our findings may explain at least in part the different manifestations of IGF-IIE overproduction in the two syndromes.

AbstractThe IGF-binding protein-4 (IGFBP-4) protease system is an important regulator of local IGF bioavailability and cell growth. Recently, the IGF-dependent IGFBP-4 protease secreted by cultured human fibroblasts was identified as pregnancy-associated plasma protein A (PAPP-A). In pregnancy serum, PAPP-A circulates as a disulfide-bound complex with the precursor form of major basic protein (pro-MBP), and in this complex PAPP-A’s proteolytic activity is not evident. In this study we analyzed the IGFBP-4 protease system in normal human fibroblasts to determine regulation outside of pregnancy. Treatment with the phorbol ester tumor promoter, β-phorbol 12,13-didecanoate (β-PDD), resulted in time-dependent inhibition of the IGF-dependent IGFBP-4 protease activity in cell-conditioned medium, which was evident at 6 h and complete by 24 h. PAPP-A mRNA was constitutively expressed in control cells, and levels were decreased only after 24 h of β-PDD treatment. Secretion of PAPP-A protein into conditioned medium did not change with β-PDD treatment. On the other hand, pro-MBP mRNA was undetectable in control human fibroblasts, and treatment with β-PDD induced pro-MBP mRNA and protein expression within 6 h. β-PDD-induced pro-MBP mRNA expression and protease inhibition were blocked with an inhibitor of RNA synthesis, actinomycin D. Actinomycin D had no effect on PAPP-A mRNA levels in the absence or presence of β-PDD. Similarly, transformation of human fibroblasts with simian virus 40 large T antigen resulted in the synthesis of pro-MBP mRNA and protein and inhibition of IGFBP-4 protease activity. Coculture of fibroblasts with cells transfected with pro-MBP cDNA resulted in inhibition of IGFBP-4 proteolytic activity without having any effect on PAPP-A synthesis. In summary, phorbol ester tumor promoters and simian virus 40 transformation regulate IGFBP-4 proteolysis in human fibroblasts through induction of a novel inhibitor of PAPP-A, pro-MBP. These findings expand our understanding of the IGFBP-4 protease system and suggest an additional level of local cell growth control.