The impact of transgenic IGF-IR overexpression on mammary development and tumorigenesis

Transgenic overexpression of the miR-200b/200a/429 cluster inhibits mammary tumor initiation

The miR-200 family consists of five members expressed as two clusters: miR-200c/141 cluster and miR-200b/200a/429 cluster. In the mammary gland, miR-200s maintain epithelial identity by decreasing the expression of mesenchymal markers leading to high expression of epithelial markers. While the loss of miR-200s is associated with breast cancer growth and metastasis the impact of miR-200 expression on mammary tumor initiation has not been investigated. Using mammary specific expression of the miR-200b/200a/429 cluster in transgenic mice, we found that elevated expression miR-200s could almost completely prevent mammary tumor development. Only 1 of 16 MTB-IGFIRba429 transgenic mice (expressing both the IGF-IR and miR-200b/200a/429 transgenes) developed a mammary tumor while 100% of MTB-IGFIR transgenic mice (expressing only the IGF-IR transgene) developed mammary tumors. RNA sequencing, qRT-PCR, and immunohistochemistry of mammary tissue from 55-day old mice found Spp1, Saa1, and Saa2 to be elevated in mammary tumors and inhibited by miR-200b/200a/429 overexpression. This study suggests that miR-200s could be used as a preventative strategy to protect women from developing breast cancer. One concern with this approach is the potential negative impact miR-200 overexpression may have on mammary function. However, transgenic overexpression of miR-200s, on their own, did not significantly impact mammary ductal development indicating the miR-200 overexpression should not significantly impact mammary function. Thus, this study provides the initial foundation for using miR-200s for breast cancer prevention and additional studies should be performed to identify strategies for increasing mammary miR-200 expression and determine whether miR-200s can prevent mammary tumor initiation by other genetic alterations.

Insulin-like growth factor-1 receptor (IGF-1R) expression on circulating tumor cells (CTCs) and metastatic breast cancer outcome: results from the TransMYME trial

PURPOSE

To evaluate the prognostic value of IGF-1R expression on circulating tumor cells (CTCs) in a prospective randomized clinical trial comparing chemotherapy plus metformin with chemotherapy alone in metastatic breast cancer (MBC) patients.

METHODS

CTCs were collected at baseline and at the end of chemotherapy. An automated sample preparation and analysis system (CellSearch) were customized for detecting IGF-1R expression. The prognostic role of CTC count and IGF-1R was assessed for PFS and OS by univariate and multivariate analyses.

RESULTS

Seventy-two out of 126 randomized patients were evaluated: 57% had ≥ 1 IGF-1R positive CTC and 37.5% ≥ 4 IGF-1R negative cells; 42% had CTC count ≥ 5/7.5 ml. At univariate analysis, the number of IGF-1R negative CTCs was strongly associated with risk of progression and death: HR 1.93 (P = 0.013) and 3.65 (P = 0.001), respectively; no association was detected between number of IGF-1R positive CTCs and PFS or OS (P = 0.322 and P = 0.840). The prognostic role of CTC count was confirmed: HR 1.69, P = 0.042 for PFS and HR 2.80 for OS, P = 0.002. By multivariate analysis, the prognostic role of the number of IGF-1R negative CTCs was maintained, while no residual prognostic role of CTC count or number of IGF-1R positive cells was found.

CONCLUSION

Loss of IGF-1R in CTCs is associated with a significantly worse outcome in MBC patients. This finding supports further evaluation for the role of IGF-1R on CTCs to improve patient stratification and to implement new targeted strategies.

CLINICAL TRIAL REGISTRATION

Clinicaltrials.gov (NCT01885013); European Clinical Trials Database (EudraCT No.2009-014,662-26).

Growth Hormone's Links to Cancer

Several components of the GH axis are involved in tumor progression, and GH-induced intracellular signaling has been strongly associated with breast cancer susceptibility in genome-wide association studies. In the general population, high IGF-I levels and low IGF-binding protein-3 levels within the normal range are associated with the development of common malignancies, and components of the GH-IGF signaling system exhibit correlations with clinical, histopathological, and therapeutic parameters in cancer patients. Despite promising findings in preclinical studies, anticancer therapies targeting the GH-IGF signaling system have led to disappointing results in clinical trials. There is substantial evidence for some degree of protection against tumor development in several animal models and in patients with genetic defects associated with GH deficiency or resistance. In contrast, the link between GH excess and cancer risk in acromegaly patients is much less clear, and cancer screening in acromegaly has been a highly controversial issue. Recent studies have shown that increased life expectancy in acromegaly patients who attain normal GH and IGF-I levels is associated with more deaths due to age-related cancers. Replacement GH therapy in GH deficiency hypopituitary adults and short children has been shown to be safe when no other risk factors for malignancy are present. Nevertheless, the use of GH in cancer survivors and in short children with RASopathies, chromosomal breakage syndromes, or DNA-repair disorders should be carefully evaluated owing to an increased risk of recurrence, primary cancer, or second neoplasia in these individuals.

Expression of insulin-like growth factor-1 receptor in circulating tumor cells of patients with breast cancer is associated with patient outcomes

In patients with breast cancer, markers of aggressiveness such as dysregulation of the insulin-like growth factor receptor (IGF1R) system and E-cadherin loss are commonly observed. Reduced IGF1R expression is correlated with decreased E-cadherin levels and increased cell motility. We assessed IGF1R and E-cadherin expression in circulating tumor cells (CTCs) in patients with breast cancer. Peripheral blood mononuclear cells of early (n = 87)- and metastatic (n = 126)-stage breast cancer patients (obtained prior to adjuvant and first-line chemotherapy) were evaluated using double immunofluorescence (IF) staining for cytokeratin (CK) and IGF1R. Triple IF using CK, IGF1R, and E-cadherin antibodies was performed in selected CTC(+) patients. IGF1R(+) CTCs were more frequently observed in early disease than in metastatic disease (86% vs 68% of CTCs, P = 0.04) stage, whereas IGF1R(-) CTCs were more common in metastatic than in early disease (32% vs 14% of CTCs, P = 0.002). 100% of CTC(+) patients with early disease, compared to 79% of those with metastatic disease, harbored IGF1R(+) CTCs (P = 0.007). Patients with early disease and exclusively IGF1R(+) CTCs had longer disease-free (P = 0.02) and overall survival (P = 0.001) compared to patients with both IGF1R(+) and IGF1R(-) CTC populations. 67% of early-stage CTC(+) patients evaluated had exclusively IGF1R(+)/E-cadherin(+) CTCs, 33% also had IGF1R(-)/E-cadherin(-) CTCs, and none had exclusively IGF1R(-)/E-cadherin(-) CTCs compared to 17%, 75%, and 8% of metastatic patients, respectively (P = 0.027). Similarly, in paired samples of patients with early disease that progressed to metastatic disease, the proportion of IGF1R(+)/E-cadherin(+) CTCs was reduced and IGF1R(-)/E-cadherin(-) CTCs were increased in the metastatic stage compared to early disease stage. IGF1R(+) CTCs are commonly detected in breast cancer, and their frequency decreases in the metastatic disease stage. IGF1R(+)/E-cadherin(+) CTCs also decrease in metastatic patients. IGF1R(+) CTCs are associated with favorable outcomes in early disease stage, suggesting that IGF1R expression is correlated with reduced metastatic potential in breast cancer.

Osteopontin regulates proliferation, apoptosis, and migration of murine claudin-low mammary tumor cells

Background

Osteopontin is a secreted phosphoglycoprotein that is expressed by a number of normal cells as well as a variety of tumor cells. With respect to breast cancer, osteopontin has been implicated in regulating tumor cell proliferation and migration/metastasis and may serve as a prognostic indicator. However it remains unclear whether osteopontin has the same impact in all breast cancer subtypes and in particular, osteopontin’s effects in claudin-low breast cancer are poorly understood.

Methods

cDNA microarrays and qRT-PCR were used to evaluate osteopontin expression in mammary tumors from MTB-IGFIR transgenic mice and cell lines derived from these tumors. siRNA was then used to determine the impact of osteopontin knockdown on proliferation, apoptosis and migration in vitro in two murine claudin-low cell lines as well as identify the receptor mediating osteopontin’s physiologic effects.

Results

Osteopontin was expressed at high levels in mammary tumors derived from MTB-IGFIR transgenic mice compared to normal mammary tissue. Evaluation of cell lines derived from different mammary tumors revealed that mammary tumor cells with claudin-low characteristic expressed high levels of osteopontin whereas mammary tumor cells with mixed luminal and basal-like features expressed lower levels of osteopontin. Reduction of osteopontin levels using siRNA significantly reduced proliferation and migration while increasing apoptosis in the claudin-low cell lines. Osteopontin’s effect appear to be mediated through a receptor containing ITGAV and not through CD44.

Conclusions

Our data suggests that mammary tumors with a mixed luminal/basal-like phenotype express high levels of osteopontin however this osteopontin appears to be largely produced by non-tumor cells in the tumor microenvironment. In contrast tumor cells with claudin-low characteristics express high levels of osteopontin and a reduction of osteopontin in these cells impaired proliferation, survival and migration.

Low-fidelity alternative DNA repair carcinogenesis theory may interpret many cancer features and anticancer strategies

We have proposed that the low-fidelity compensatory backup alternative DNA repair pathways drive multistep carcinogenesis. Here, we apply it to interpret the clinical features of cancer, such as mutator phenotype, tissue specificity, age specificity, diverse types of cancers originated from the same type of tissue, cancer susceptibility of patients with DNA repair-defective syndromes, development of cancer only for a selected number of individuals among those that share the same genetic defect, invasion and metastasis. Clinically, the theory predicts that to improve the efficacy of molecular targeted or synthetic lethal therapy, it may be crucial to inhibit the low-fidelity compensatory alternative DNA repair either directly or by blocking the signal transducers of the sustained microenvironmental stress.

Low-fidelity compensatory backup alternative DNA repair pathways may unify current carcinogenesis theories

The somatic mutation carcinogenesis theory has dominated for decades. The alternative theory, tissue organization field theory, argues that the development of cancer is determined by the surrounding microenvironment. However, neither theory can explain all features of cancer. As cancers share the features of uncontrolled proliferation and genomic instability, they are likely to have the same pathogenesis. It has been found that various DNA repair pathways within a cell crosstalk with one another, forming a DNA repair network. When one DNA repair pathways is defective, the others may work as compensatory backups. The latter pathways are explored for synthetic lethal anticancer therapy. In this article, we extend the concept of compensatory alternative DNA repair to unify the theories. We propose that the microenvironmental stress can activate low-fidelity compensatory alternative DNA repair, causing mutations. If the mutation occurs to a DNA repair gene, this secondarily mutated gene can lead to even more mutated genes, including those related to other DNA repair pathways, eventually destabilizing the genome. Therefore, the low-fidelity compensatory alternative DNA repair may mediate microenvironment-dependent carcinogenesis. The proposal seems consistent with the view of evolution: the environmental stress causes mutations to adapt to the changing environment.

Crosstalk of the Insulin-Like Growth Factor Receptor with the Wnt Signaling Pathway in Breast Cancer

The insulin-like growth factor system has long been considered a pathway that promotes cell proliferation, survival, and transformation, and is thus a promoter of tumorigenesis. However, recent failure of clinical trials for IGF-1R inhibitors reveals the need for a better understanding of how this pathway functions in specific tumor subtypes. Ongoing studies are designed to uncover biomarkers and downstream targets to enhance therapeutic strategies. Other approaches in specific tumor models reveal complex interactions between IGF signaling and other tumor initiating pathways. Here, we review relevant background and recent studies suggesting that inhibiting the IGF-1R can amplify Wnt and Notch signaling pathways in a model of triple negative breast cancer.

Inactivation of RARβ inhibits Wnt1-induced mammary tumorigenesis by suppressing epithelial-mesenchymal transitions

Retinoic acid receptor β (RARβ) has been proposed to act as a tumor suppressor in breast cancer. In contrast, recent data have shown that RARβ promotes ERBB2-induced mammary gland tumorigenesis through remodeling of the stromal compartment and activation of cancer-associated fibroblasts. However, it is currently unknown whether RARβ oncogenic activity is specific to ERBB2-induced tumors, or whether it influences the initiation and progression of other breast cancer subtypes. Accordingly, we set out to investigate the involvement of RARβ in basal-like breast cancer using mouse mammary tumor virus (MMTV)-wingless-related integration site 1 (Wnt1)-induced mammary gland tumorigenesis as a model system. We found that compared with wild type mice, inactivation of Rarb resulted in a lengthy delay in Wnt1-induced mammary gland tumorigenesis and in a significantly slower tumor growth rate. Ablation of Rarb altered the composition of the stroma, repressed the activation of cancer-associated fibroblasts, and reduced the recruitment of inflammatory cells and angiogenesis. Reduced expression of IGF-1 and activity of its downstream signaling pathway contribute to attenuate EMT in the Rarb-null tumors. Our results show that, in the absence of retinoid signaling via RARβ, reduced IGF-1 signaling results in suppression of epithelial-mesenchymal transition and delays tumorigenesis induced by the Wnt1 oncogene. Accordingly, our work reinforces the concept that antagonizing RARβ-dependent retinoid signaling could provide a therapeutic avenue to treat poor outcome breast cancers.

Association between insulin-like growth factor-1 receptor (IGF1R) negativity and poor prognosis in a cohort of women with primary breast cancer

Background

Resistance towards endocrine therapy is a great concern in breast cancer treatment and may partly be explained by the activation of compensatory signaling pathways. The aim of the present study was to investigate if the insulin-like growth factor-1 receptor (IGF1R) signaling pathway was activated or deregulated in breast cancer patients and to explore if any of the markers were prognostic, with or without adjuvant tamoxifen. This signaling pathway has been suggested to cause estrogen independent cell growth and thus contribute to resistance to endocrine treatment in estrogen receptor (ER) positive breast cancer.

Methods

The protein expression of IGF1R, phosphorylated Mammalian Target of Rapamycin (p-mTOR) and phosphorylated S6 ribosomal protein (p-S6rp) were investigated by immunohistochemistry using tissue microarrays in two patient cohorts. Cohort I (N = 264) consisted of mainly postmenopausal women with stage II breast cancer treated with tamoxifen for 2 years irrespective of ER status. Cohort II (N = 206) consisted of mainly medically untreated, premenopausal patients with node-negative breast cancer. Distant disease-free survival (DDFS) at 5 years was used as end-point for survival analyses.

Results

We found that lower IGF1R expression was associated with worse prognosis for tamoxifen treated, postmenopausal women (HR = 0.70, 95% CI = 0.52 – 0.94, p = 0.016). The effect was seen mainly in ER-negative patients where the prognostic effect was retained after adjustment for other prognostic markers (adjusted HR = 0.49, 95% CI = 0.29 – 0.82, p = 0.007). Expression of IGF1R was associated with ER positivity (p < 0.001) in the same patient cohort.

Conclusions

Our results support previous studies indicating that IGF1R positivity reflects a well differentiated tumor with low metastatic capacity. An association between lack of IGF1R expression and worse prognosis was mainly seen in the ER-negative part of Cohort I. The lack of co-activation of downstream markers (p-mTOR and p-S6rp) in the IGF1R pathway suggested that the prognostic effect was not due to complete activation of this pathway. Thus, no evidence could be found for a compensatory function of IGF1R signaling in the investigated cohorts.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-794) contains supplementary material, which is available to authorized users.

Clinical pathological characteristics and prognostic analysis of diabetic women with luminal subtype breast cancer

This study selected luminal-type breast cancer patients as the study subjects. The patients were divided into groups according to the presence of diabetes and the types of medication used, and the patients' clinicopathological characteristics and prognostic indicators were explored. A total of 5,785 patients with luminal-type breast cancer admitted to Tianjin Medical University Cancer Institute and Hospital between January 2002 and December 2006 were selected as the study subjects. The subjects included 680 breast cancer patients with diabetes and 5,105 breast cancer patients without diabetes. The patients were divided into Luminal A, Luminal B (high ki67), and Luminal B (her-2/neu+) subtypes. Each subtype was further divided into a metformin group, a non-metformin group, and a nondiabetic group. The research indicators included breast cancer mortality, age, body mass index (BMI), amenorrhea, the presence of cardiovascular and cerebrovascular disease, pathological stage, pathological type, lymph node involvement, vessel carcinoma embolus, and the chemotherapy and endocrine regimen. A Kaplan-Meier analysis was conducted to analyze the differences in breast cancer mortality rates among the groups. The Cox proportional hazard model was adopted to detect independent factors related to prognosis. Kaplan-Meier univariate analysis showed that for the Luminal A, Luminal B (high ki67), and Luminal B (her-2/neu+) subtypes, the cancer-specific mortality rates differed significantly among the metformin, non-metformin, and nondiabetic groups. The 5-year survival rates were 94%, 82%, and 91% (P = 0.002); 93.5%, 81%, and 89% (P < 0.001); and 84%, 77%, and 83% (P = 0.035) for the subtypes within each group, respectively. Cox regression multivariate analysis showed that compared with the metformin group, all three subtypes of the, the non-metformin group showed poorer prognosis (hazard ratio [HR], 3.579; 95% confidence interval [CI], 1.506-8.506 [P = 0.004]; HR, 3.232; 95% CI, 1.839-5.678 [P < 0.001]; HR, 2.034; 95% CI,1.019-4.059 [P = 0.044] for Luminal A, Luminal B (high ki67), and Luminal B (her-2/neu+, respectively). Compared with the metformin group, the diabetic group showed poorer prognosis only for the Luminal B (high ki67) subtype (HR, 1.762; 95% CI, 1.033-3.005 [P = 0.038]). In addition, for the Luminal A, Luminal B (high ki67), and Luminal B (her-2/neu+) subgroups, there was a higher proportion of elderly patients (P < 0.001) and postmenopausal patients (P < 0.001) in the metformin and non-metformin groups than in the nondiabetic group. Moreover, the probability of having cardiovascular and cerebrovascular disease was also higher (P < 0.001) in the metformin and non-metformin groups. For the Luminal B (high ki67) and Luminal B (her-2/neu +) subgroups, there was a higher proportion of obese patients in the metformin and non-metformin groups (P < 0.001). In terms of clinical characteristics, for the Luminal B (high ki67) subtype, the proportion of patients with invasive ductal carcinoma was lower in the non-metformin group than in the other two groups (P = 0.001). In both the metformin and non-metformin groups, the proportion of T3/4 patients was higher (P < 0.001), the proportion of patients with lymph node metastasis was higher (P = 0.001), and the proportion of patients with vessel carcinoma embolus was higher (P = 0.001) compared with the nondiabetic group. In conclusion, compared with the metformin group, the non-metformin group had a poorer prognosis for all subtypes of luminal breast cancer. In the diabetic group, only patients with the Luminal B (high ki67) subtype exhibited a poorer prognosis. Therefore, different diabetes medication may have a different impact on the prognosis of different subtypes of luminal breast cancer.

Clinical pathological characteristics and prognostic analysis of 1,013 breast cancer patients with diabetes

The purpose of this study was to investigate the clinical, pathological, and prognostic characteristics of breast cancer patients with diabetes. In total, the study included 1,013 breast cancer patients with diabetes and 4,621 breast cancer patients without diabetes. Patients with diabetes were further divided into the metformin- and nonmetformin-treated subgroups. The percentage of elderly patients (P < 0.001), obese patients (P < 0.001), and menopausal patients (P < 0.001) as well as the percentage of patients with cardio-cerebrovascular complications (P < 0.001), negative PR (P < 0.001) expression, or low Ki67 expression (P = 0.001) tended to be higher in the diabetic group. In addition, these patients had later pathological stages (P < 0.001), more lymph node metastasis (P = 0.014), and a lower percentage of them were on the anthracycline-based chemotherapy regimen (P = 0.003). The diabetic group was further divided into the metformin and nonmetformin-treated subgroups. The pairwise comparison between the metformin-treated subgroup and the control group did not show a significant difference in the pathological stages (P = 0.0079). However, the HER-2 positive rate tended to be lower in the metformin-treated subgroup than in the nonmetformin-treated subgroup (P = 0.002). No significant difference was found in the lymph node status between the nonmetformin-treated subgroup and the control group (P = 0.057), while the nonmetformin-treated subgroup was associated with higher HER-2 positive expression (P = 0.002). The median follow-up time for this study was 68 months (10-120 months). In Kaplan-Meier analysis, The diabetic group predicted worse survival compared with the control group (P < 0.001) with 5-year survival rates of 79 and 82 %, respectively. The breast cancer mortality rates in the metformin-treated subgroup, the nonmetformin-treated subgroup, and the control group were significantly different (long-rank test, P < 0.001), and the 5-year survival rates were 88, 73, and 82 %, respectively. As shown in the multivariate survival analysis using Cox's regression model, compared with the control group, the metformin-treated subgroup was associated with lower mortality risk (HR 0.762; 95 % CI 0.6-0.968; P = 0.026), whereas the nonmetformin-treated subgroup was associated with higher mortality risk (HR 1.708; 95 % CI 1.461-1.997; P < 0.001). In conclusion, the diabetic group is associated with poor prognosis. Compared with the control group, the metformin-treated subgroup is associated with better clinical outcomes, while nonmetformin-treated subgroup with poorer prognosis. The selection of different antidiabetic drugs may impact the prognosis of breast cancer patients with diabetes.

Mammary tumor regression elicited by Wnt signaling inhibitor requires IGFBP5

Wnt ligand-driven tumor growth is inhibited by the soluble Wnt inhibitor Fzd8CRD, but the mechanism through which this effect is mediated is unknown. In the MMTV-Wnt1 mouse model, regression of mammary tumors by Fzd8CRD treatment coincides with an acute and strong induction of insulin-like growth factor (IGF)-binding protein IGFBP5, an antagonist of IGF signaling that mediates involution of mammary gland in females after offspring are weaned. In this study, we show that repression of this IGF inhibitory pathway is crucial for Wnt-driven growth of mammary tumors. We found that IGFBP5 regulation was mediated by the β-catenin-dependent Wnt pathway. Wnt, in addition to IGF ligands, facilitated tumor growth by paracrine communication among tumor cells. In addition, Fzd8CRD caused precocious induction of IGFBP5 in normal mammary glands undergoing involution, implying an acceleration of the involution process by inhibition of Wnt signaling. The molecular and phenotypic parallel between tumor regression and mammary gland involution suggests that Wnt-driven mammary tumors use the same growth mechanism as proliferating normal mammary glands.

Fetal alcohol exposure increases mammary tumor susceptibility and alters tumor phenotype in rats

BACKGROUND

Altered fetal programming because of a suboptimal in utero environment has been shown to increase susceptibility to many diseases later in life. This study examined the effect of alcohol exposure in utero on N-nitroso-N-methylurea (NMU)-induced mammary cancer risk during adulthood.

METHODS

Study 1: Pregnant Sprague Dawley rats were fed a liquid diet containing 6.7% ethanol (alcohol-fed), an isocaloric liquid diet (pair-fed), or rat chow ad libitum (ad lib-fed) from day 11 to 21 of gestation. At birth, female pups were cross-fostered to ad lib-fed control dams. Adult offspring were given an I.P. injection of NMU at a dose of 50 mg/kg body weight. Mammary glands were palpated for tumors twice a week, and rats were euthanized at 23 weeks postinjection. Study 2: To investigate the role of estradiol (E2), animals were exposed to the same in utero treatments but were not given NMU. Serum was collected during the preovulatory phase of the estrous cycle.

RESULTS

At 16 weeks postinjection, overall tumor multiplicity was greater in the offspring from the alcohol-fed group compared to the control groups, indicating a decrease in tumor latency. At study termination, 70% of all animals possessed tumors. Alcohol-exposed animals developed more malignant tumors and more estrogen receptor-α-negative tumors relative to the control groups. In addition, IGF-binding protein-5 (IGFBP-5) mRNA and protein were decreased in tumors of alcohol-exposed animals. Study 2 showed that alcohol-fed animals had significantly increased circulating E2 when compared to either control group.

CONCLUSIONS

These data indicate that alcohol exposure in utero increases susceptibility to mammary tumorigenesis in adulthood and suggest that alterations in the IGF and E2 systems may play a role in the underlying mechanism.

Golgi calcium pump secretory pathway calcium ATPase 1 (SPCA1) is a key regulator of insulin-like growth factor receptor (IGF1R) processing in the basal-like breast cancer cell line MDA-MB-231

Calcium signaling is a key regulator of pathways important in tumor progression, such as proliferation and apoptosis. Most studies assessing altered calcium homeostasis in cancer cells have focused on alterations mediated through changes in cytoplasmic free calcium levels. Here, we show that basal-like breast cancers are characterized by an alteration in the secretory pathway calcium ATPase 1 (SPCA1), a calcium pump localized to the Golgi. Inhibition of SPCA1 in MDA-MB-231 cells produced pronounced changes in cell proliferation and morphology in three-dimensional culture, without alterations in sensitivity to endoplasmic reticulum stress induction or changes in global calcium signaling. Instead, the effects of SPCA1 inhibition in MDA-MB-231 cells reside in altered regulation of calcium-dependent enzymes located in the secretory pathway, such as proprotein convertases. Inhibition of SPCA1 produced a pronounced alteration in the processing of insulin-like growth factor receptor (IGF1R), with significantly reduced levels of functional IGF1Rβ and accumulation of the inactive trans-Golgi network pro-IGF1R form. These studies identify for the first time a calcium transporter associated with the basal-like breast cancer subtype. The pronounced effects of SPCA1 inhibition on the processing of IGF1R in MDA-MB-231 cells independent of alterations in global calcium signaling also demonstrate that some calcium transporters can regulate the processing of proteins important in tumor progression without major alterations in cytosolic calcium signaling. Inhibitors of SPCA1 may offer an alternative strategy to direct inhibitors of IGF1R and attenuate the processing of other proprotein convertase substrates important in basal breast cancers.

ErbB2 enhances mammary tumorigenesis, oncogene-independent recurrence and metastasis in a model of IGF-IR-mediated mammary tumorigenesis

Background

The type I insulin-like growth factor receptor (IGF-IR) and ErbB2 (Her-2) are receptor tyrosine kinases implicated in human breast cancer. Both proteins are currently the subject of targeted therapeutics that are used in the treatment of breast cancer or which are in clinical trials. The focus of this study was to utilize our inducible model of IGF-IR overexpression to explore the interaction of these two potent oncogenes.

Results

ErbB2 was overexpressed in our RM11A cell line, a murine tumor cell line that overexpresses human IGF-IR in an inducible manner. ErbB2 conferred an accelerated tumor onset and increased tumor incidence after injection of RM11A cells into the mammary glands of syngeneic wild type mice. This was associated with increased proliferation immediately after tumor cell colonization of the mammary gland; however, this effect was lost after tumor establishment. ErbB2 overexpression also impaired the regression of established RM11A tumors following IGF-IR downregulation and enhanced their metastatic potential.

Conclusion

This study has revealed that even in the presence of vast IGF-IR overexpression, a modest increase in ErbB2 can augment tumor establishment in vivo, mediate resistance to IGF-IR downregulation and facilitate metastasis. This supports the growing evidence suggesting a possible advantage of using IGF-IR and ErbB2-directed therapies concurrently in the treatment of breast cancer.

IGF-I during primiparous pregnancy and maternal risk of breast cancer

Previously, we reported that insulin-like growth factor (IGF)-I during early pregnancy is positively associated with maternal risk of breast cancer. To further explore this association, we designed a new study limited to women who donated a blood sample during their first pregnancy ending with childbirth. A case-control study was nested within the Northern Sweden Maternity Cohort in which repository since 1975, serum specimens remaining after early pregnancy screening for infectious diseases had been preserved. Study subjects were selected among women who donated a blood sample during the full-term pregnancy that led to the birth of their first child. Two hundred and forty-four women with invasive breast cancer were eligible. Two controls, matching the index case for age and date at blood donation were selected (n = 453). IGF-I was measured in serum samples on an Immulite 2000 analyzer. Conditional logistic regression was used to estimate odds ratios and 95% confidence intervals. A significant positive association of breast cancer with IGF-I was observed, with OR of 1.73 (95% CI: 1.14-2.63) for the top tertile, P < 0.009. Subgroup analyses did not indicate statistical heterogeneity of the association by ages at sampling and diagnosis or by lag time to cancer diagnosis, although somewhat stronger associations with risk were observed in women < or = age 25 at index pregnancy and for cases diagnosed within 15 years of blood donation. The results of the study add further evidence for an adverse effect of elevated IGF-I concentrations during early reproductive life on risk of breast cancer.

Prolactin enhances insulin-like growth factor I receptor phosphorylation by decreasing its association with the tyrosine phosphatase SHP-2 in MCF-7 breast cancer cells

Normal mammary development requires coordinated interactions of numerous factors, including prolactin (PRL) and insulin-like growth factor I (IGF-I), both of which have also been implicated in breast cancer pathogenesis and progression. We previously reported that PRL and IGF-I synergize in breast cancer cells to activate ERK1/2 and AKT, leading to increased proliferation, survival, and invasion. Intriguingly, PRL co-treatment with IGF-I augments IGF-I receptor (IGF-IR) phosphorylation 2-fold higher than IGF-I alone. Here, we showed the importance of the tyrosine phosphatase SHP-2 in this cross-talk using pharmacological inhibition and small interfering RNA. SHP-2 recruitment to IGF-IR was significantly attenuated by PRL co-treatment. Src family kinase activity was required for IGF-IR association with SHP-2, ligand-induced IGF-IR internalization, and PRL-enhanced IGF-IR phosphorylation. Inhibition of internalization, via knockdown of the GTPase, dynamin-2, prevented not only IGF-IR dephosphorylation, but also PRL-enhanced IGF-IR phosphorylation. Consistently, PRL diminished IGF-I-induced IGF-IR internalization, which may result from reduced SHP-2 association with IGF-IR, because we demonstrated an essential role for SHP-2 in IGF-IR internalization. Together, these findings describe a novel mechanism of cross-talk between PRL and IGF-I in breast cancer cells, with implications for our understanding of tumor progression and potential therapeutic strategies.