Mutations in the Ras-Raf Axis underlie the prognostic value of CD133 in colorectal cancer

Intra-tumor heterogeneity from a cancer stem cell perspective

Tumor heterogeneity represents an ongoing challenge in the field of cancer therapy. Heterogeneity is evident between cancers from different patients (inter-tumor heterogeneity) and within a single tumor (intra-tumor heterogeneity). The latter includes phenotypic diversity such as cell surface markers, (epi)genetic abnormality, growth rate, apoptosis and other hallmarks of cancer that eventually drive disease progression and treatment failure. Cancer stem cells (CSCs) have been put forward to be one of the determining factors that contribute to intra-tumor heterogeneity. However, recent findings have shown that the stem-like state in a given tumor cell is a plastic quality. A corollary to this view is that stemness traits can be acquired via (epi)genetic modification and/or interaction with the tumor microenvironment (TME). Here we discuss factors contributing to this CSC heterogeneity and the potential implications for cancer therapy.

LGR5 and CD133 as prognostic and predictive markers for fluoropyrimidine-based adjuvant chemotherapy in colorectal cancer

BACKGROUND

Expression of leucine-rich-repeat-containing G-protein-coupled receptor 5 (LGR5) gene is associated with a metastatic phenotype and poor prognosis in colorectal cancer (CRC). CD133 expression is a putative cancer stem cell marker and a proposed prognostic marker in CRC, whereas the predictive value of CD133 expression for effect of adjuvant chemotherapy in CRC is unclear.

MATERIAL AND METHODS

For the study of LGR5 mRNA and CD133 expression, tissue microarrays from 409 primary CRC stage II and III tumors, where patients had been randomized to adjuvant chemotherapy or surgery only, were available. LGR5 mRNA and CD133 expression were assessed by in situ hybridization (ISH) and immunohistochemistry (IHC), respectively. LGR5 mRNA and CD133 expression as prognostic and predictive markers were evaluated by univariate and multivariate analyses.

RESULTS

For all CRC patients, positive LGR5 mRNA and CD133 expression were associated with classic adenocarcinoma histology type (p = 0.001 and p = 0.014, respectively). Positive LGR5 mRNA expression was also associated with smaller tumor diameter for CRC stage II (p = 0.005), but not for CRC stage III (p = 0.054). For CRC stage II, lack of LGR5 mRNA expression was associated with longer time to recurrence (TTR) in Kaplan-Meier (p = 0.045) and in multivariate Cox analysis (HR 0.27, 95% CI 0.08-0.95, p = 0.041). For colon cancer stage III patients, lack of CD133 expression was associated with better effect of adjuvant chemotherapy (p = 0.016) in Kaplan-Meier univariate analysis, but the interaction between CD133 and adjuvant chemotherapy was not statistically significant in multivariate analysis (HR 0.59, 95% CI 0.18-1.89, p = 0.374).

CONCLUSION

LGR5 mRNA expression is a prognostic factor for CRC stage II patients, whereas the value of CD133 expression as prognostic and predictive biomarker is inconclusive.

Gene signatures of estrogen and progesterone receptor pathways predict the prognosis of colorectal cancer

The associations of estrogen receptor (ER) and progesterone receptor (PR) pathways with the prognosis of colorectal cancer (CRC) are still controversial. The aim of this study was to readdress these issues by introducing a gene signature-based approach to semiquantitate pathway activity. In this approach, the ER and PR pathway activities in CRC were computed based on the expression profiles of the signature genes of ER and PR pathways, respectively. The results showed that the ER pathway activity was progressively significantly decreased from normal colorectal mucosa, colorectal adenoma to CRC. ER pathway signaling was a favorable factor for the presence of microsatellite stability (MSS) in CRC in seven cohorts tested, while was an unfavorable factor for cancer recurrence in all four CRC cohorts tested (n = 1122; overall HR: 0.311, 95% CI: 0.199-0.488, P < 0.001). Subset stratification in stage II patients showed that ER pathway remained significantly inversely associated with recurrence. PR pathway was also suppressed in colorectal tumors and inversely associated with recurrence of CRC, but to a much lesser extent than ER pathway. Moreover, the inverse association of PR pathway with cancer recurrence was more likely observed in CRC with high ER pathway activity, suggesting the interactions between the two pathways. PR pathway was not associated with MSS in CRC, but it was more significant than ER pathway associated with advance cancer stages and cancer response to adjuvant chemotherapy. These results suggested the potential application of the gene signatures of ER and PR pathways, especially the former, as novel markers for prognosis and management of CRC.

Up-regulation of stem cell markers by P21-activated kinase 1 contributes to 5-fluorouracil resistance of colorectal cancer

Cancer stem cells (CSC) are tumorigenic and resistant to chemotherapy. In colorectal cancer (CRC), CSCs have been identified by the expression of specific markers, including CD44, Bmi1 and Nanog. Although p21-activated kinase 1 (PAK1), acting downstream of Ras, stimulates Wnt/β-catenin signaling and is known to play an important role in CRC development and progression, the role of PAK1 in the expression of CSC markers has not previously been investigated. The effect of PAK1 over-expression, knockdown or inhibition on the expression or alteration (in the case of CD44) of CSC markers in human CRC cell lines was measured by immunofluorescence and Western blotting. The effect of PAK1 modulation on tumorigenesis, and on resistance to treatment with 5-fluorouracil (5-FU), was measured by sphere formation in vitro and by growth of xenografted tumors in vivo. The results show that PAK1 activity correlated with the expression of CSC markers and the CD44 isoform profile, and with tumor growth both in vitro and in vivo. Furthermore PAK overexpression partially overcame the inhibition of CRC growth by 5-FU, and PAK inhibition was synergistic with 5-FU treatment. Our findings lay the foundation for a combination therapy in which PAK1 inhibitors targeting CSCs may be combined with conventional 5-FU-based chemotherapy for the treatment of CRC.

Key role of MEK/ERK pathway in sustaining tumorigenicity and in vitro radioresistance of embryonal rhabdomyosarcoma stem-like cell population

BACKGROUND

The identification of signaling pathways that affect the cancer stem-like phenotype may provide insights into therapeutic targets for combating embryonal rhabdomyosarcoma. The aim of this study was to investigate the role of the MEK/ERK pathway in controlling the cancer stem-like phenotype using a model of rhabdospheres derived from the embryonal rhabdomyosarcoma cell line (RD).

METHODS

Rhabdospheres enriched in cancer stem like cells were obtained growing RD cells in non adherent condition in stem cell medium. Stem cell markers were evaluated by FACS analysis and immunoblotting. ERK1/2, myogenic markers, proteins of DNA repair and bone marrow X-linked kinase (BMX) expression were evaluated by immunoblotting analysis. Radiation was delivered using an x-6 MV photon linear accelerator. Xenografts were obtained in NOD/SCID mice by subcutaneously injection of rhabdosphere cells or cells pretreated with U0126 in stem cell medium.

RESULTS

MEK/ERK inhibitor U0126 dramatically prevented rhabdosphere formation and down-regulated stem cell markers CD133, CXCR4 and Nanog expression, but enhanced ALDH, MAPK phospho-active p38 and differentiative myogenic markers. By contrast, MAPK p38 inhibition accelerated rhabdosphere formation and enhanced phospho-active ERK1/2 and Nanog expression. RD cells, chronically treated with U0126 and then xeno-transplanted in NOD/SCID mice, delayed tumor development and reduced tumor mass when compared with tumor induced by rhabdosphere cells. U0126 intraperitoneal administration to mice bearing rhabdosphere-derived tumors inhibited tumor growth . The MEK/ERK pathway role in rhabdosphere radiosensitivity was investigated in vitro. Disassembly of rhabdospheres was induced by both radiation or U0126, and further enhanced by combined treatment. In U0126-treated rhabdospheres, the expression of the stem cell markers CD133 and CXCR4 decreased and dropped even more markedly following combined treatment. The expression of BMX, a negative regulator of apoptosis, also decreased following combined treatment, which suggests an increase in radiosensitivity of rhabdosphere cells.

CONCLUSIONS

Our results indicate that the MEK/ERK pathway plays a prominent role in maintaining the stem-like phenotype of RD cells, their survival and their innate radioresistance. Thus, therapeutic strategies that target cancer stem cells, which are resistant to traditional cancer therapies, may benefit from MEK/ERK inhibition combined with traditional radiotherapy, thereby providing a promising therapy for embryonal rhabdomyosarcoma.

Bidirectional interconversion of stem and non-stem cancer cell populations: A reassessment of theoretical models for tumor heterogeneity

Resolving the origin of intratumor heterogeneity has proven to be one of the central challenges in cancer research during recent years. Two theoretical models explaining the emergence of intratumor heterogeneity have come to dominate cancer biology literature: the clonal evolution model and the hierarchical/cancer stem cell model. Recently, a plastic model that combines elements of both the clonal and the hierarchical model has gained traction. Basically, this model proposes that cancer stem cells engage in bidirectional interconversion with non-stem cells, thereby providing the missing link between the 2 conventional models. Confirming bidirectional interconversion as a hallmark of cancer is a crucial step in understanding tumor heterogeneity and has important therapeutic implications. In this review, current methodologies and theoretical and empirical evidence regarding bidirectional interconversion will be discussed.

Colorectal cancer stem cells: from the crypt to the clinic

Since their first discovery, investigations of colorectal cancer stem cells (CSCs) have revealed some unexpected properties, including a high degree of heterogeneity and plasticity. By exploiting a combination of genetic, epigenetic, and microenvironmental factors, colorectal CSCs metastasize, resist chemotherapy, and continually adapt to a changing microenvironment, representing a formidable challenge to cancer eradication. Here, we review the current understanding of colorectal CSCs, including their origin, relationship to stem cells of the intestine, phenotypic characterization, and underlying regulatory mechanisms. We also discuss limitations to current preclinical models of colorectal cancer and how understanding CSC plasticity can improve the development of clinical strategies.

Biomarkers and signaling pathways of colorectal cancer stem cells

The progression of colorectal cancer is commonly characterized by accumulation of genetic or epigenetic abnormalities, altering regulation of gene expression as well as normal protein structures and functions. Nonetheless, there are some questions that remain to be elucidated, such as the origin of cancer cells and populations of cells initiating and propagating tumor development. Currently, there are two rival theories describing the process of carcinogenesis. One is the stochastic model, arguing that any cell is capable of initiating and triggering the development of cancer. Meanwhile, the cancer stem cell model hypothesizes that only a small fraction of stem cells possesses cancer-promoting properties. Typically, colorectal cancer stem cells (CSCs) share the same molecular signaling profiles with normal stem cells or embryonic stem cells, such as Wnt, Notch, TGF-β, and Hedgehog. Nevertheless, CSCs differ from normal stem cells and the bulk of tumor cells in their tumorigenic potential and susceptibility to chemotherapeutic drugs. This may be a possible explanation of the high percentage of cancer recurrence in patients who underwent chemotherapeutic treatment and surgery. This review article focuses on the colorectal cancer stem cell biomarkers and the role of upregulated signaling pathways implicated in the initiation and progression of colorectal cancer.

Photochemical internalisation, a minimally invasive strategy for light-controlled endosomal escape of cancer stem cell-targeting therapeutics

Despite progress in radio-, chemo- and photodynamic-therapy (PDT) of cancer, treatment resistance still remains a major problem for patients with aggressive tumours.

BRAF vs RAS oncogenes: are mutations of the same pathway equal? Differential signalling and therapeutic implications

As the increased knowledge of tumour heterogeneity and genetic alterations progresses, it exemplifies the need for further personalized medicine in modern cancer management. Here, the similarities but also the differential effects of RAS and BRAF oncogenic signalling are examined and further implications in personalized cancer diagnosis and therapy are discussed. Redundant mechanisms mediated by the two oncogenes as well as differential regulation of signalling pathways and gene expression by RAS as compared to BRAF are addressed. The implications of RAS vs BRAF differential functions, in relevant tumour types including colorectal cancer, melanoma, lung cancer are discussed. Current therapeutic findings and future viewpoints concerning the exploitation of RAS-BRAF-pathway alterations for the development of novel therapeutics and efficient rational combinations, as well as companion tests for relevant markers of response will be evaluated. The concept that drug-resistant cells may also display drug dependency, such that altered dosing may prevent the emergence of lethal drug resistance posed a major therapy hindrance.

Stem cell dynamics in homeostasis and cancer of the intestine

Intestinal stem cells (ISCs) and colorectal cancer (CRC) biology are tightly linked in many aspects. It is generally thought that ISCs are the cells of origin for a large proportion of CRCs and crucial ISC-associated signalling pathways are often affected in CRCs. Moreover, CRCs are thought to retain a cellular hierarchy that is reminiscent of the intestinal epithelium. Recent studies offer quantitative insights into the dynamics of ISC behaviour that govern homeostasis and thereby provide the necessary baseline parameters to begin to apply these analyses during the various stages of tumour development.

Molecular profiling in colorectal cancer: current state of play and future directions

SUMMARY In the era of molecular scientific discovery, there is a continuing gap between our growing scientific knowledge and its utility at the bedside. This phenomenon probably occurs more frequently in colorectal cancer than in other cancer streams, with thousands of scientific studies having produced only a handful of molecular interventions. This review examines our current practices of molecular profiling in colorectal cancer and the scientific research that may impact on this area in the future.

Cancer stem cells in colorectal cancer from pathogenesis to therapy: Controversies and perspectives

Colorectal cancer remains one of the most common and lethal malignancies worldwide despite the use of various therapeutic strategies. A better understanding of the mechanisms responsible for tumor initiation and progression is essential for the development of novel, more powerful therapies. The traditional, so-called “stochastic model” of tumor development, which assumes that each cancer cell is tumorigenic, has been deeply challenged during the past decade by the identification of cancer stem cells (CSCs), a biologically distinct subset of cells within the bulk of tumor mass. This discovery led to the development of the hierarchical model of tumorigenesis which assumes that only CSCs have the ability to initiate tumor growth, both at primary and metastatic sites. This model implies that the elimination of all CSCs is fundamental to eradicate tumors and that failure to do so might be responsible for the occurrence of relapses and/or metastases frequently observed in the clinical management of colorectal cancer patients. Identification and isolation of CSCs is essential for a better understanding of their role in the tumorigenetic process and for the development of CSC-specific therapies. Several methods have been used for this purpose and many efforts have been focused on the identification of specific CSC-surface markers. This review provides an overview of the proposed roles of CSC in human colorectal tumorigenesis focusing on the most important molecules identified as CSC-specific markers in colorectal cancer and on the potential strategies for the development of CSC-targeted therapy.

CD133 facilitates epithelial-mesenchymal transition through interaction with the ERK pathway in pancreatic cancer metastasis

BACKGROUND

Pancreatic cancer is a lethal disease due to the high incidence of metastasis at the time of detection. CD133 expression in clinical pancreatic cancer correlates with poor prognosis and metastasis. However, the molecular mechanism of CD133-regulated metastasis remains unclear. In recent years, epithelial-mesenchymal transition (EMT) has been linked to cancer invasion and metastasis. In the present study we investigated the role of CD133 in pancreatic cancer metastasis and its potential regulatory network.

METHODS

A highly migratory pancreatic cancer cell line, Capan1M9, was established previously. After shRNA was stable transducted to knock down CD133 in Capan1M9 cells, gene expression was profiled by DNA microarray. Orthotopic, splenic and intravenous transplantation mouse models were set up to examine the tumorigenesis and metastatic capabilities of these cells. In further experiments, real-time RT-PCR, Western blot and co-immunoprecipitate were conducted to evaluate the interactions of CD133, Slug, N-cadherin, ERK1/2 and SRC.

RESULTS

We found that CD133+ human pancreatic cancer cells were prone to generating metastatic nodules in in vivo models using immunodeficient mice. In contrast, CD133 knockdown suppressed cancer invasion and metastasis in vivo. Gene profiling analysis suggested that CD133 modulated mesenchymal characteristics including the expression of EMT-related genes, such as Slug and N-cadherin. These genes were down-regulated following CD133 knockdown. Moreover, CD133 expression could be modulated by the extracellular signal-regulated kinase (ERK)1/2 and SRC signaling pathways. The binding of CD133 to ERK1/2 and SRC acts as an indispensable mediator of N-cadherin expression.

CONCLUSIONS

These results demonstrate that CD133 plays a critical role in facilitating the EMT regulatory loop, specifically by upregulating N-cadherin expression, leading to the invasion and metastasis of pancreatic cancer cells. Our study provides a novel insight into the function of CD133 in the EMT program and a better understanding of the mechanism underlying the involvement of CD133 in pancreatic cancer metastasis.

New molecules and old drugs as emerging approaches to selectively target human glioblastoma cancer stem cells

Despite relevant progress obtained by multimodal treatment, glioblastoma (GBM), the most aggressive primary brain tumor, is still incurable. The most encouraging advancement of GBM drug research derives from the identification of cancer stem cells (CSCs), since these cells appear to represent the determinants of resistance to current standard therapies. The goal of most ongoing studies is to identify drugs able to affect CSCs biology, either inducing selective toxicity or differentiating this tumor cell population into nontumorigenic cells. Moreover, the therapeutic approach for GBM could be improved interfering with chemo- or radioresistance mechanisms, microenvironment signals, and the neoangiogenic process. During the last years, molecular targeted compounds such as sorafenib and old drugs, like metformin, displayed interesting efficacy in preclinical studies towards several tumors, including GBM, preferentially affecting CSC viability. In this review, the latest experimental results, controversies, and prospective application concerning these promising anticancer drugs will be discussed.

CD133: A cancer stem cells marker, is used in colorectal cancers

Colorectal cancer is one of the most common malignant tumors worldwide. A model of cancer development involving cancer stem cells has been put forward because it provides a possible explanation of tumor hierarchy. Cancer stem cells are characterized by their proliferation, tumorigenesis, differentiation, and self-renewal capacities, and chemoradiotherapy resistance. Due to the role of cancer stem cells in tumor initiation and treatment failure, studies of cancer stem cell markers, such as CD133, have been of great interest. CD133, a five-transmembrane glycoprotein, is widely used as a marker to identify and isolate colorectal cancer stem cells. This marker has been investigated to better understand the characteristics and functions of cancer stem cells. Moreover, it can also be used to predict tumor progression, patient survival, chemoradiotherapy resistance and other clinical parameters. In this review, we discuss the use of CD133 in the identification of colorectal cancer stem cell, which is currently controversial. Although the function of CD133 is as yet unclear, we have discussed several possible functions and associated mechanisms that may partially explain the role of CD133 in colorectal cancers. In addition, we focus on the prognostic value of CD133 in colorectal cancers. Finally, we predict that CD133 may be used as a possible target for colorectal cancer treatment.

Clinical significance of microRNA-93 downregulation in human colon cancer

AIM

MicroRNA-93 (miR-93) has been shown to suppress proliferation and colony formation of colon cancer stem cells. The aim of this study was to examine the expression pattern and prognostic value of miR-93 in patients with colon cancer.

MATERIALS AND METHODS

A quantitative real-time PCR analysis was carried out to detect the expression levels of miR-93 in 138 paired samples of tumoral and nontumoral colon tissues diagnosed with colon cancer. Associations of miR-93 expression with clinicopathological parameters and survival were also examined.

RESULTS

miR-93 expression was significantly decreased in tumoral compared with nontumoral colon tissues (P<0.001). Low miR-93 expression was significantly correlated with advanced tumor stage (P=0.02), positive nodal metastasis (P=0.006), and positive distant metastases (P=0.01). In addition, Kaplan-Meier survival analysis by Cox regression showed that low miR-93 expression [hazard ratio (HR), 10.2; 95% confidence interval (CI), 1.9-42.8, P=0.003] was associated closely with poor overall survival in patients with colon cancer. Moreover, multivariate analysis showed that miR-93 decreased expression (HR, 4.3; 95% CI, 0.8-17.2, P=0.02), advanced tumor stage (HR, 3.1; 95% CI, 0.2-13.9, P=0.04), positive nodal metastasis (HR, 4.1; 95% CI, 0.7-16.8, P=0.02), and positive distant metastases (HR, 3.7; 95% CI, 0.5-14.1, P=0.03) were independent risk factors for overall survival in patients with colon cancer.

CONCLUSION

Our data show for the first time that the downregulation of miR-93 was significantly correlated with unfavorable clinicopathologic features and short overall survival in patients with colon cancer, suggesting that decreased expression of miR-93 be used as a novel prognostic factor for this disease.

CD133 expression and the prognosis of colorectal cancer: a systematic review and meta-analysis

Objective

CD133 has recently been reported as a marker of cancer stem-like cells in colorectal cancer (CRC). However, its predictive value in CRC still remains controversial. In this study, we aimed to evaluate the association between the expression of CD133 and clinicopathological features and the outcome of CRC patients by performing a meta-analysis.

Methods

A comprehensive literature search for relevant studies published up to December 2012 was performed using PubMed, MEDLINE and ISI Web of Science. Only articles in which CD133 antigen was detected in situ localisation by immunohistochemical staining were included. This meta-analysis was done using RevMan 4.2 software.

Results

We found that a total of 15 studies involving 810 CD133-high and 1487 CD133-low patients met the inclusion criteria for the analysis of 5-year overall survival (OS) rate. In a random-effects model, the results showed that CD133-high expression in colorectal cancer was an independent prognostic marker correlating with both OS rate (RR = 0.67, 95%CI 0.54–0.82, P<0.01) and disease free survival (DFS) rate (RR = 0.71, 95%CI 0.52–0.96, P = 0.03). CD133-high expression was also associated with more T3,4 tumor invasion, N positive and vascular invasion cases, corresponding to a risk difference of 1.12 (95%CI 1.01–1.23, P = 0.03), 1.31 (95%CI 1.06–1.63, P = 0.01) and 1.24 (95%CI 1.08–1.41, P<0.01), respectively. However, when types of histology, lymphatic invasion and distant metastasis were considered, CD133 overexpression was not significantly related with these clinicopathological parameters.

Conclusion

Our meta-analysis results suggest that CD133 is an efficient prognostic factor in CRC. Higher CD133 expression is significantly associated with poorer clinical outcome and some clinicopathological factors such as T category, N category and vascular invasion in CRC patients.

New Insights into the CD133 (Prominin-1) Expression in Mouse and Human Colon Cancer Cells

Following its discovery as a cancer stem cell marker, CD133 has been widely studied for its role in colorectal tumorigenesis. Indeed, colon cancer remains one of the major causes of cancer-related disease and death worldwide, and there is a strong need for an improvement of current diagnostic, prognostic, and therapeutic strategies. Thus, efforts have been devoted to try to understand whether CD133 might play a role in human colorectal tumorigenesis and might contribute to a better management of colon cancer patients. This chapter reviews the current knowledge on CD133 expression in normal and cancer colon tissues, both in humans and mice, discussing apparently conflicting data reported in the two species. Moreover, a great attention is devoted to the available information regarding the functional role of CD133 in colon cancer cells. Finally, the proposed clinical applications of CD133, as a prognostic and/or predictive marker as well as a target for novel antineoplastic strategies in colorectal cancer, are discussed. Overall, the available data support a potential important role of CD133 as cancer stem cell marker in colon cancer cells and warrant future studies to verify its potential use in the routine clinical management of colon cancer patients.

Metformin selectively affects human glioblastoma tumor-initiating cell viability: A role for metformin-induced inhibition of Akt

Cancer stem cell theory postulates that a small population of tumor-initiating cells is responsible for the development, progression and recurrence of several malignancies, including glioblastoma. In this perspective, tumor-initiating cells represent the most relevant target to obtain effective cancer treatment. Metformin, a first-line drug for type II diabetes, was reported to possess anticancer properties affecting the survival of cancer stem cells in breast cancer models. We report that metformin treatment reduced the proliferation rate of tumor-initiating cell-enriched cultures isolated from four human glioblastomas. Metformin also impairs tumor-initiating cell spherogenesis, indicating a direct effect on self-renewal mechanisms. Interestingly, analyzing by FACS the antiproliferative effects of metformin on CD133-expressing subpopulation, a component of glioblastoma cancer stem cells, a higher reduction of proliferation was observed as compared with CD133-negative cells, suggesting a certain degree of cancer stem cell selectivity in its effects. In fact, glioblastoma cell differentiation strongly reduced sensitivity to metformin treatment. Metformin effects in tumor-initiating cell-enriched cultures were associated with a powerful inhibition of Akt-dependent cell survival pathway, while this pathway was not affected in differentiated cells. The specificity of metformin antiproliferative effects toward glioblastoma tumor-initiating cells was confirmed by the lack of significant inhibition of normal human stem cells (umbilical cord-derived mesenchymal stem cells) in vitro proliferation after metformin exposure. Altogether, these data clearly suggest that metformin exerts antiproliferative activity on glioblastoma cells, showing a higher specificity toward tumor-initiating cells, and that the inhibition of Akt pathway may represent a possible intracellular target of this effect.

Expectation of success following noncontingent punishment in introverts and extraverts

Recent findings indicate that extraverts are more likely than introverts to continue responding in the face of punishment and frustrating nonreward (Newman & Kosson, 1984; Tiggemann, Winefield, & Brebner, 1982). The current study investigates whether extraverts' expectations for success are, similarly, resistant to interruption and alteration. To test this hypothesis, 50 introverted and 50 extraverted male undergraduates were exposed to pretreatment with either a 50% level of noncontingent reward or a 50% level of noncontingent punishment. As predicted, there were significant Group X Pretreatment interactions on all dependent measures. In comparison to those introverts who received the punishment pretreatment, extraverts exposed to the same pretreatment placed larger wagers on their ability to succeed, and reported higher levels of perceived control. In addition, relative to their estimates for the pretreatment task, extraverts exposed to noncontingent punishment increased their expectation for success, whereas introverts exposed to noncontingent punishment decreased their performance expectations. No differences were observed between the two groups following pretreatment with noncontingent reward. The results suggest that extraverts are characterized by a distinctive reaction to punishment involving response facilitation as opposed to response inhibition.