G-helix of maspin mediates effects on cell migration and adhesion

SERPINB5 promotes colorectal cancer invasion and migration by promoting EMT and angiogenesis via the TNF-α/NF-κB pathway

This study aimed to investigate the role of SERPINB5 in colorectal cancer (CRC). We established knockdown and overexpression models of SERPINB5 in CRC cells and conducted bioinformatics analysis to assess the clinicopathological significance of SERPINB5 expression in CRC patients. Human CRC cells were transfected with LV-SERPINB5 and sh-SERPINB5 lentivirus for subsequent functional and mechanistic studies. Results showed that high SERPINB5 expression correlated positively with CEA levels, N stage and lymphatic infiltration, while displaying a negative correlation with progression-free survival. Overexpression of SERPINB5 in CRC cells upregulated the expression of TNF-α, p-NF-κB/p65, N-cadherin, MMP2 and MMP9, accompanied by decreased E-cadherin expression. In addition, SERPINB5 overexpression enhanced the migration, invasion, and proliferation of CRC cells. Furthermore, overexpression of SERPINB5 in CRC cells increased VEGFA expression, and the conditioned medium from SERPINB5-overexpressing CRC cells promoted tube formation of HUVECs. Conversely, overexpression of SERPINB5 in HUVECs decreased VEGFA expression and inhibited tube formation. Notably, these changes in CRC cells were reversed by QNZ, a specific inhibitor of the TNF-α/NF-κB pathway. In summary, our findings revealed that high SERPINB5 expression correlated with poor progression-free survival in CRC patients. Moreover, SERPINB5 could induce EMT and angiogenesis by activating the TNF-α/NF-κB pathway, thereby promoting the invasion and migration of CRC cells.

Integrating the tumor-suppressive activity of Maspin with p53 in retuning the epithelial homeostasis: A working hypothesis and applicable prospects

Epithelial malignant transformation and tumorous development were believed to be closely associated with the loss of its microenvironment integrity and homeostasis. The tumor-suppressive molecules Maspin and p53 were demonstrated to play a crucial role in body epithelial and immune homeostasis. Downregulation of Maspin and mutation of p53 were frequently associated with malignant transformation and poor prognosis in various human cancers. In this review, we focused on summarizing the progress of the molecular network of Maspin in studying epithelial tumorous development and its response to clinic treatment and try to clarify the underlying antitumor mechanism. Notably, Maspin expression was reported to be transcriptionally activated by p53, and the transcriptional activity of p53 was demonstrated to be enhanced by its acetylation through inhibition of HDAC1. As an endogenous inhibitor of HDAC1, Maspin possibly potentiates the transcriptional activity of p53 by acetylating the p53 protein. Hereby, it could form a “self-propelling” antitumor mechanism. Thus, we summarized that, upon stimulation of cellular stress and by integrating with p53, the aroused Maspin played the epigenetic surveillant role to prevent the epithelial digressional process and retune the epithelial homeostasis, which is involved in activating host immune surveillance, regulating the inflammatory factors, and fine-tuning its associated cell signaling pathways. Consequentially, in a normal physiological condition, activation of the above “self-propelling” antitumor mechanism of Maspin and p53 could reduce cellular stress (e.g., chronic infection/inflammation, oxidative stress, transformation) effectively and achieve cancer prevention. Meanwhile, designing a strategy of mimicking Maspin’s epigenetic regulation activity with integrating p53 tumor-suppressive activity could enhance the chemotherapy efficacy theoretically in a pathological condition of cancer.

Maspin binds to cardiolipin in mitochondria and triggers apoptosis

A central question in cell biology is how cells respond to stress signals and biochemically regulate apoptosis. One critical pathway involves the change of mitochondrial function and release of cytochrome c to initiate apoptosis. In response to apoptotic stimuli, we found that maspin-a noninhibitory member of the serine protease inhibitor superfamily-translocates from the cytosol to mitochondria and binds to cardiolipin in the inner mitochondrial membrane. Biolayer interferometry assay revealed that recombinant maspin binds cardiolipin with an apparent Kd,of ∼15.8 μM and competes with cytochrome c (apparent Kd of ∼1.31 μM) for binding to cardiolipin-enriched membranes. A hydrophobic, lysine-rich domain in maspin consists of 27 aa, is located at position 268-294, and is responsible for the interaction of this protein with cardiolipin. Depletion of cardiolipin in cells significantly prevents maspin binding to the inner mitochondrial membrane and decreases cytochrome c release and apoptosis. Alteration to maspin's cardiolipin binding domain changes its ability to bind cardiolipin, and tumor cells expressing this mutant have a low frequency of apoptosis. We propose a model of apoptosis in which maspin binds to cardiolipin, displaces cytochrome c from the membrane, and facilitates its release to the cytoplasm.-Mahajan, N., Hoover, B., Rajendram, M., Shi, H. Y., Kawasaki, K., Weibel, D. B., Zhang, M. Maspin binds to cardiolipin in mitochondria and triggers apoptosis.

Potential of Protein-based Anti-metastatic Therapy with Serpins and Inter α-Trypsin Inhibitors

In this review we summarize the principles of anti-metastatic therapy with selected serpin family proteins, such as pigment epithelial-derived factor (PEDF) and maspin, as well as inter α-trypsin inhibitor (IαIs) light chains (bikunin) and heavy chains (ITIHs). Case-by-case, antimetastatic activity may be dependent or independent of the protease-inhibitory activity of the corresponding proteins. We discuss the incidence of target deregulation in different tumor entities, mechanisms of deregulation, context-dependent functional issues as well as in vitro and in vivo target validation studies with transfected tumor cells or recombinant protein as anti-metastatic agents. Finally, we comment on possible clinical evaluation of these proteins in adjuvant therapy.

Recombinant human maspin inhibits high glucose-induced oxidative stress and angiogenesis of human retinal microvascular endothelial cells via PI3K/AKT pathway

Maspin is known as a tumor suppressor and a potent angiogenesis inhibitor, however, its effects on proliferative diabetic retinopathy (PDR) have not been fully elucidated. This study aimed at evaluating the effects of maspin on high glucose-induced oxidative stress and angiogenesis in human retinal microvascular endothelial cells (HRMECs). Herein, HRMECs were treated with 0.25, 0.5, or 1 µM recombinant human maspin in the presence of 30 mM glucose, and their proliferation, tube formation, and oxidative stress responses were further detected. Our results revealed that maspin inhibited the high glucose-induced proliferation, migration, and tube formation of HRMECs. Maspin also decreased reactive oxygen species, nitric oxide level, and increased glutathione S-transferase activity in HRMECs. Meanwhile, maspin reduced the mRNA and protein levels of hypoxia-inducible factor-1α and vascular endothelial growth factor in high glucose-stimulated cells in a dose-dependent manner. Additionally, the high glucose-induced elevation of phosphorylated phosphoinositide-3-kinase (p-PI3K) and phosphorylated AKT was also suppressed by maspin. In summary, our data suggest that maspin inhibits high glucose-induced proliferation, oxidative stress, and angiogenesis of HRMECs at least by modulating the PI3K/AKT pathway. Maspin may be a potential therapeutic agent for the prevention and treatment of PDR.

SERPINB5 Expression: Association with CCRT Response and Prognostic Value in Rectal Cancer

Background: Due to the varying characteristics and conflicting outcomes on the overall survival of rectal cancer patients, many studies have been undertaken to determine various prognostic and predictive factors for the mainstay treatment of CCRT followed by surgery. Cancer cell motility contributes to tumor invasion, migration and eventually metastasis. However, the genes associated with cell motility (i.e., GO:0048870) have not been systemically evaluated in rectal cancers. Methods: A comparative analysis of gene expression profiles was applied to the transcriptomic dataset (GSE35452) with a focus on genes associated with cell motility (GO:0048870), where SERPINB5 was recognized as the most significantly up-regulated gene. Tumor samples from 172 primary rectal cancer patients who underwent neoadjuvant CCRT followed by surgical resection were collected. Immunohistochemistry was used to semi-quantitatively assess the expression level of SERPINB5 protein. Statistical analyses of SERPINB5 expression and various clinicopathological features as well as survival were then performed. Results: High immunoreactivity of SERPINB5 was significantly linked to pre- and post-CCRT advanced disease, lymphovascular invasion, and poor response to CCRT (all P ≤ 0.015). SERPINB5 overexpression was not only negatively associated with disease-specific survival (DSS), local recurrence-free survival (LRFS) and metastasis-free survival (MeFS) rates in univariate analyses but also was an independent prognostic factor for DSS and MeFS in rectal cancer patients (all P ≤ 0.043). Conclusion: SERPINB5 may play an important role in rectal cancer progression and response to neoadjuvant CCRT and serve as a novel prognostic factor.

The Opportunity of Precision Medicine for Breast Cancer With Context-Sensitive Tumor Suppressor Maspin

To improve the precision of molecular diagnosis and to develop and guide targeted therapies of breast cancer, it is essential to determine the mechanisms that underlie the specific tumor phenotypes. To this end, the application of a snapshot of gene expression profile for breast cancer diagnosis and prognosis is fundamentally challenged since the tissue-based data are derived from heterogonous cell types and are not likely to reflect the dynamics of context-dependent tumor progression and drug sensitivity. The intricate network of epithelial differentiation program can be concertedly controlled by tumor suppressor maspin, a homologue of clade B serine protease inhibitors (serpin), through its multifaceted molecular interactions in multiple subcellular localizations. Unlike most other serpins that are expressed in multiple cell types, maspin is epithelial specific and has distinct roles in luminal and myoepithelial cells. Endogenously expressed maspin has been found in the nucleus and cytoplasm, and detected on the surface of cell membrane. It is also secreted free and as an exosomal cargo protein. Research in the field has led to the identification of the maspin targets and maspin-associated molecules, as well as the structural determinants of its suppressive functions. The current review discusses the possibility for maspin to serve as a cell type-specific and context-sensitive marker to improve the precision of breast cancer diagnosis and prognosis. These advancements further suggest a new window of opportunity for designing novel maspin-based chemotherapeutic agents with improved anti-cancer potency. J. Cell. Biochem. 118: 1639-1647, 2017. © 2017 Wiley Periodicals, Inc.

IKKα inibition by a glucosamine derivative enhances Maspin expression in osteosarcoma cell line

Chronic inflammation has been associated to cancer development by the alteration of several inflammatory pathways, such as Nuclear Factor-κB pathway. In particular, IκB kinase α (IKKα), one of two catalytic subunit of IKK complex, has been described to be associated to cancer progression and metastasis in a number of cancers. The molecular mechanism by which IKKα affects cancer progression is not yet completely clarified, anyway an association between IKKα and the expression of Maspin (Mammary Serine Protease Inhibitor or SerpinB5), a tumor suppressor protein, has been described. IKKα shuttles between cytoplasm and nucleus, and when is localized into the nuclei, IKKα regulates the expression of several genes, among them Maspin gene, whose expression is repressed by high amount of nuclear IKKα. Considering that high levels of Maspin have been associated with reduced metastatic progression, it could be hypothesized that the repression of IKKα nuclear translocation could be associated with the repression of metastatic phenotype. The present study is aimed to explore the ability of a glucosamine derivative, 2-(N-Carbobenzyloxy)l-phenylalanylamido-2-deoxy-β-d-glucose (NCPA), synthesized in our laboratory, to stimulate the production of Maspin in an osteosarcoma cell line, 143B. Immunofluorescence and Western blotting experiments showed that NCPA is able to inhibit IKKα nuclear translocation, and to stimulate Maspin production. Moreover, in association with stimulation of Maspin production we found the decrease of β1 Integrin expression, the down-regulation of metalloproteases MMP-9 and MMP-13 production and cell migration inhibition. Taking in account that β1 Integrin and MMP-9 and -13 have been correlated with the invasiveness of osteosarcoma, considering that NCPA affects the invasiveness of 143B cell line, we suggest that this molecule could affect the osteosarcoma metastatic ability.

1.45 Å resolution structure of SRPN18 from the malaria vector Anopheles gambiae

Serine protease inhibitors (serpins) in insects function within development, wound healing and immunity. The genome of the African malaria vector, Anopheles gambiae, encodes 23 distinct serpin proteins, several of which are implicated in disease-relevant physiological responses. A. gambiae serpin 18 (SRPN18) was previously categorized as non-inhibitory based on the sequence of its reactive-center loop (RCL), a region responsible for targeting and initiating protease inhibition. The crystal structure of A. gambiae SRPN18 was determined to a resolution of 1.45 Å, including nearly the entire RCL in one of the two molecules in the asymmetric unit. The structure reveals that the SRPN18 RCL is extremely short and constricted, a feature associated with noncanonical inhibitors or non-inhibitory serpin superfamily members. Furthermore, the SRPN18 RCL does not contain a suitable protease target site and contains a large number of prolines. The SRPN18 structure therefore reveals a unique RCL architecture among the highly conserved serpin fold.

Identification of novel peptide motifs in the serpin maspin that affect vascular smooth muscle cell function

Maspin is a non-inhibitory member of the serpin family that affects cell behaviours related to migration and survival. We have previously shown that peptides of the isolated G α-helix (G-helix) domain of maspin show bioactivity. Migration, invasion, adhesion and proliferation of vascular smooth muscle cells (VSMC) are important processes that contribute to the build-up of atherosclerotic plaques. Here we report the use of functional assays of these behaviours to investigate whether other maspin-derived peptides impact directly on VSMC; focusing on potential anti-atherogenic properties. We designed 18 new peptides from the structural moieties of maspin above ten amino acid residues in length and considered them beside the existing G-helix peptides. Of the novel peptides screened those with the sequences of maspin strand 4 and 5 of beta sheet B (S4B and S5B) reduced VSMC migration, invasion and proliferation, as well as increasing cell adhesion. A longer peptide combining these consecutive sequences showed a potentiation of responses, and a 7-mer contained all essential elements for functionality. This is the first time that these parts of maspin have been highlighted as having key roles affecting cell function. We present evidence for a mechanism whereby S4B and S5B act through ERK1/2 and AMP-activated protein kinase (AMPK) to influence VSMC responses.

Maspin-related Orchestration of Aggressiveness of Gastric Cancer

BACKGROUND AND STUDY AIM

Although some hypotheses have been postulated on the genesis of gastric cancer (GC), the origin of this disease remains unclear. The aim of this study was to develop a hypothesis about gastric carcinogenesis based on our experience in the field of GC and on published reports on about 28 studies in the field of subcellular maspin expression in GC. In 180 cases of GC, the clinicopathologic features were correlated with the results obtained after paired immunohistochemical stains (tumor/normal mucosa) with 15 antibodies: E-cadherin, HER-2, VEGF, CD31, CD105, COX-2, maspin, bax, bcl-2, p53, Ki67, MLH-1, MSH-2, Mena protein, and vimentin.

RESULTS

Cytoplasmic maspin was observed in foveolar cells with intestinal metaplasia, whereas mixed (combined nuclear-cytoplasmic) expressions were more characteristic of the intramucosal foci of signet-ring cells and dysplastic cells. The tumor cells that expressed cytoplasmic maspin were mostly intestinal type bax/COX-2/Mena/E-cadherin-positive differentiated adenocarcinomas with nodular growth and more superficial invasion. The nuclear shift of maspin was more frequent in HER-2/p53-positive intestinal type adenocarcinomas with diffuse architecture at the invasion front, as well as for node-positive poorly cohesive carcinomas. Loss of maspin expression induced a higher risk of distant metastases, without differences in the survival rate.

CONCLUSIONS

In GC with associated metaplasia, cytoplasmic maspin is predominant; the nuclear shift induces local aggressiveness and risk of node metastases, whereas total loss can indicate a risk of distant metastases. In GC without associated metaplasia, nuclear expression of maspin is retained, indicating a more aggressive behavior.

Effects of Noninhibitory Serpin Maspin on the Actin Cytoskeleton: A Quantitative Image Modeling Approach

Recent developments in quantitative image analysis allow us to interrogate confocal microscopy images to answer biological questions. Clumped and layered cell nuclei and cytoplasm in confocal images challenges the ability to identify subcellular compartments. To date, there is no perfect image analysis method to identify cytoskeletal changes in confocal images. Here, we present a multidisciplinary study where an image analysis model was developed to allow quantitative measurements of changes in the cytoskeleton of cells with different maspin exposure. Maspin, a noninhibitory serpin influences cell migration, adhesion, invasion, proliferation, and apoptosis in ways that are consistent with its identification as a tumor metastasis suppressor. Using different cell types, we tested the hypothesis that reduction in cell migration by maspin would be reflected in the architecture of the actin cytoskeleton. A hybrid marker-controlled watershed segmentation technique was used to segment the nuclei, cytoplasm, and ruffling regions before measuring cytoskeletal changes. This was informed by immunohistochemical staining of cells transfected stably or transiently with maspin proteins, or with added bioactive peptides or protein. Image analysis results showed that the effects of maspin were mirrored by effects on cell architecture, in a way that could be described quantitatively.

RGD and polyhistidine tumor homing peptides potentiates the action of human Maspin as an antineoplastic candidate

Maspin, a non-inhibitory member of serine protease family, acts as an effective tumor suppressor by inhibiting cell inhesion and mobility. We found that exogenous wild-type rMaspin had a low effect on tumor growth in vivo. However, when the peptide Arg-Gly-Asp-hexahistidine (RGD-6His) was introduced into rMaspin, the modified rMaspin showed significant inhibitory activity in angiogenic assays and tumor-bearing animal models. Overall, our data suggested that both the RGD and hexahistidine fragments contributed to improve the fusion protein activity and polyhistidine peptide could be considered as flexible linker to separate RGD and Maspin moieties to avoid function interference. Besides, it is an efficient tag to achieve purified recombinant proteins. Furthermore, rMaspin fusing with RGD and hexahistidine could be a viable anticancer candidate.

An in silico model to demonstrate the effects of Maspin on cancer cell dynamics

Most cancer treatments efficacy depends on tumor metastasis suppression, where tumor suppressor genes play an important role. Maspin (Mammary Serine Protease Inhibitor), an non-inhibitory serpin has been reported as a potential tumor suppressor to influence cell migration, adhesion, proliferation and apoptosis in in vitro and in vivo experiments in last two decades. Lack of computational investigations hinders its ability to go through clinical trials. Previously, we reported first computational model for maspin effects on tumor growth using artificial neural network and cellular automata paradigm with in vitro data support. This paper extends the previous in silico model by encompassing how maspin influences cell migration and the cell-extracellular matrix interaction in subcellular level. A feedforward neural network was used to define each cell behavior (proliferation, quiescence, apoptosis) which followed a cell-cycle algorithm to show the microenvironment impacts over tumor growth. Furthermore, the model concentrates how the in silico experiments results can further confirm the fact that maspin reduces cell migration using specific in vitro data verification method. The data collected from in vitro and in silico experiments formulates an unsupervised learning problem which can be solved by using different clustering algorithms. A density based clustering technique was developed to measure the similarity between two datasets based on the number of links between instances. Our proposed clustering algorithm first finds the nearest neighbors of each instance, and then redefines the similarity between pairs of instances in terms of how many nearest neighbors share the two instances. The number of links between two instances is defined as the number of common neighbors they have. The results showed significant resemblances with in vitro experimental data. The results also offer a new insight into the dynamics of maspin and establish as a metastasis suppressor gene for further molecular research.

Different maspin functions in the lung adenocarcinoma A549 and SPC-A1 cell lines

Mammary serine protease inhibitor (maspin) is a tumor suppressor gene that is silenced in the majority of cancer cells during metastatic progression by transcriptional and epigenetic mechanisms. The function of maspin in non‑small cell lung cancer cells (NSCLC) has not been clearly defined. In the present study, the expression of maspin in NSCLC cell lines, in particular, the adenocarcinoma cell lines, was heterogeneous. While the expression levels of maspin in PC‑9 and H460 cell lines were intact, the expression of maspin in the A549 and SPC‑A1 cells was hardly detected. Ectopic expression of maspin in A549 cells carrying the K‑ras gene point mutation significantly inhibited cell migration and invasion abilities, which was associated with downregulated expression of matrix metalloproteinase‑2 and integrin β1. Ectopic expression of maspin in SPC‑A1 cells harboring the wild‑type K‑ras gene predominantly affected cell growth via targeting the AKT signaling molecules. Maspin functions differently in lung adenocarcinoma cells, possibly due to the varied molecular characteristics.

Supramolecular assembly of multifunctional maspin-mimetic nanostructures as a potent peptide-based angiogenesis inhibitor

Aberrant angiogenesis plays a large role in pathologies ranging from tumor growth to macular degeneration. Anti-angiogenic proteins have thus come under scrutiny as versatile, potent therapeutics but face problems with purification and tissue retention. We report here on the synthesis of supramolecular nanostructures that mimic the anti-angiogenic activity of maspin, a class II tumor suppressor protein. These maspin-mimetic nanostructures are formed via self-assembly of small peptide amphiphiles containing the g-helix motif of maspin. Using tubulogenesis assays with human umbilical vein endothelial cells, we demonstrate that maspin-mimetic nanostructures show anti-angiogenic activity at concentrations that are significantly lower than those necessary for the g-helix peptide. Furthermore, in vivo assays in the chick chorioallantoic membrane show maspin-mimetic nanostructures to be effective over controls at inhibiting angiogenesis. Thus, the nanostructures investigated here offer an attractive alternative to the use of anti-angiogenic recombinant proteins in the treatment of cancer or other diseases involving abnormal blood vessel formation.

Decreased maspin combined with elevated vascular endothelial growth factor C is associated with poor prognosis in non-small cell lung cancer

BACKGROUND

This study aimed to investigate the clinical significance of the combination of maspin and vascular endothelial growth factor (VEGF)-C expression in the prognosis of non-small cell lung cancer (NSCLC).

METHODS

Immunohistochemistry was performed to assay the expression of maspin and VEGF-C in primary tumor tissues, metastatic, and non-metastatic lymph nodes in 98 NSCLC patients. Survival analysis was determined by Kaplan-Meier curves.

RESULTS

The positive expression rate of maspin was 26.5% (26/98) in NSCLC primary tumor tissues, significantly associated with histological type (P = 0.005) and the absence of nodal metastasis (P < 0.001). The expression of maspin in primary tumor tissues was stronger than metastatic lymph nodes of the N1 group (P = 0.048), while the metastatic lymph nodes of the N1 group had a stronger maspin expression than the N2 group (P = 0.008). In survival analysis, a positive expression of maspin of the N1 lymph node was also found to be an independent positive prognostic factor in overall survival (P = 0.003). We also found that decreased maspin combined with elevated VEGF-C is associated with a poor prognosis for disease-free survival (P = 0.019).

CONCLUSION

Our results suggest that positive expression of maspin might significantly inhibit nodal metastasis in NSCLC. Decreased maspin combined with elevated VEGF-C might be associated with a poor prognosis in NSCLC.

Identification of an intrinsic determinant critical for maspin subcellular localization and function

Maspin, a multifaceted tumor suppressor, belongs to the serine protease inhibitor superfamily, but only inhibits serine protease-like enzymes such as histone deacetylase 1 (HDAC1). Maspin is specifically expressed in epithelial cells and it is differentially regulated during tumor progression. A new emerging consensus suggests that a shift in maspin subcellular localization from the nucleus to the cytoplasm stratifies with poor cancer prognosis. In the current study, we employed a rational mutagenesis approach and showed that maspin reactive center loop (RCL) and its neighboring sequence are critical for maspin stability. Further, when expressed in multiple tumor cell lines, single point mutation of Aspartate(346) (D(346)) to Glutamate (E(346)), maspin(D346E), was predominantly nuclear, whereas wild type maspin (maspin(WT)) was both cytoplasmic and nuclear. Evidence from cellular fractionation followed by immunological and proteomic protein identification, combined with the evidence from fluorescent imaging of endogenous proteins, fluorescent protein fusion constructs, as well as bimolecular fluorescence complementation (BiFC) showed that the increased nuclear enrichment of maspin(D346E) was, at least in part, due to its increased affinity to HDAC1. Maspin(D346E) was also more potent than maspin(WT) as an HDAC inhibitor. Taken together, our evidence demonstrates that D(346) is a critical cis-element in maspin sequence that determines the molecular context and subcellular localization of maspin. A mechanistic model derived from our evidence suggests a new window of opportunity for the development of maspin-based biologically competent HDAC inhibitors for cancer treatment.

Glucose-regulated protein 78 mediates hormone-independent prostate cancer progression and metastasis through maspin and COX-2 expression

Glucose-regulated protein 78 (GRP78) plays an essential role in embryonic development and in the progression and therapeutic resistance of many cancers. However, little is known about the function of GRP78 in hormone-independent prostate cancer. Here, we found that the expression levels of GRP78 were higher in PC-3 cells than in DU-145 cells. When the expression of GRP78 was silenced using a GRP78-specific small interfering RNA in PC-3 cells, the growth rate and adhesive ability were reduced. Cell migration was dramatically decreased in GRP78-depleted cells. Dissection of the involved signal pathways revealed that maspin expression was upregulated after silencing GRP78 expression. The upregulation of maspin and downregulation of COX-2 may cause the decrease in cell proliferation and migration observed after silencing GRP78 expression. Silencing GRP78 expression may suppress the proliferation, adhesion, and migration of prostate cancer cells via maspin and COX-2 regulation.

Maspin: molecular mechanisms and therapeutic implications

Maspin, a non-inhibitory member of the serine protease inhibitor superfamily, has been characterized as a tumor suppressor gene in multiple cancer types. Among the established anti-tumor effects of Maspin are the inhibition of cancer cell invasion, attachment to extracellular matrices, increased sensitivity to apoptosis, and inhibition of angiogenesis. However, while significant experimental data support the role of Maspin as a tumor suppressor, clinical data regarding the prognostic implications of Maspin expression have led to conflicting results. This highlights the need for a better understanding of the context dependencies of Maspin in normal biology and how these are perturbed in the context of cancer. In this review, we outline the regulation and roles of Maspin in normal and developmental biology while discussing novel evidence and emerging theories related to its functions in cancer. We provide insight into the immense therapeutic potential of Maspin and the challenges related to its successful clinical translation.

Role of maspin in cancer

Maspin (mammary serine protease inhibitor), is a member of the serine protease inhibitor/non-inhibitor superfamily. Its expression is down-regulated in breast, prostate, gastric and melanoma cancers but over-expressed in pancreatic, gallbladder, colorectal, and thyroid cancers suggesting that maspin may play different activities in different cell types. However, maspin expression seems to be correlated with better prognosis in prostate, bladder, lung, gastric, colorectal, head and neck, thyroid and melanoma cancer. In breast and ovarian cancer maspin significance is associated with its subcellular localization: nucleus maspin expression correlates with a good prognosis, whilst in pancreatic cancer it predicts a poor prognosis. Since tumor metastasis requires the detachment and invasion of tumor cells through the basement membrane and stroma, a selectively increased adhesion by the presence of maspin may contribute to the inhibition of tumor metastasis. Furthermore the different position of maspin inside the cell or its epigenetic modifications may explain the different behavior of the expression of maspin between tumors. The expression of maspin might be useful as a prognostic and possibly predictive factor for patients with particular types of cancer and data can guide physicians in selecting therapy. Its expression in circulating tumor cells especially in breast cancer, could be also useful in clinical practice along with other factors, such as age, comorbidities, blood examinations in order to select the best therapy to be carried out. Focusing on the malignancies in which maspin showed a positive prognostic value, therapeutic approaches studied so far aimed to re-activate a dormant tumor suppressor gene by designed transcription factors, to hit the system that inhibits the expression of maspin, to identify natural substances that can determine the activation and the expression of maspin or possible “molecules binds” to introduce maspin in cancer cell and gene therapy capable of up-regulating the maspin in an attempt to reduce primarily the risk of metastasis.

Further studies in these directions are necessary to better define the therapeutic implication of maspin.

An emerging role for the nuclear localization of maspin in the suppression of tumor progression and metastasis

Maspin, a member of the serpin family of serine protease inhibitors, was originally identified as a tumor suppressor that is expressed in normal mammary epithelial cells but is reduced or absent in breast carcinomas. Early enthusiasm for maspin as a biomarker for disease progression has been tempered by clinical data that associates maspin with favourable outcomes in some studies and poor prognosis in others. Here, we review all of the published clinical studies for maspin in breast and ovarian cancers and propose that the apparent discordance between clinical reports is a consequence of differential cellular distribution of maspin. Indeed, it was thought that an extracellular pool of maspin possessed tumor suppressor activity, acting by inhibiting migration and increasing cell adhesion. Recent evidence from our group and others indicates, however, that the nuclear localization of maspin in cancer cells is necessary for its tumor suppressor activity. We provide additional data here to demonstrate that nuclear-localized maspin binds to chromatin and is required to effectively prevent cells from metastasizing. Our knowledge of other serpins that localize to the nucleus should help to inform future studies of nuclear maspin. Elucidation of the molecular mechanisms regulating the localization and activities of maspin should pave the way for the development of improved diagnostics and therapies for cancer.

Maspin, the molecular bridge between the plasminogen activator system and beta1 integrin that facilitates cell adhesion

Maspin is a non-inhibitory serine protease inhibitor (serpin) that influences many cellular functions including adhesion, migration, and invasion. The underlying molecular mechanisms that facilitate these actions are still being elucidated. In this study we determined the mechanism by which maspin mediates increased MCF10A cell adhesion. Utilizing competition peptides and mutation analyses, we discovered two unique regions (amino acid residues 190-202 and 260-275) involved in facilitating the increased adhesion function of maspin. In addition, we demonstrate that the urokinase-type plasminogen activator (uPA)/uPA receptor (uPAR) complex is required for the localization and adhesion function of maspin. Finally, we showed that maspin, uPAR, and β1 integrin co-immunoprecipitate, suggesting a novel maspin-uPA-uPAR-β1 integrin mega-complex that regulates mammary epithelial cell adhesion.