Peroxynitrite in the tumor microenvironment changes the profile of antigens allowing escape from cancer immunotherapy

Cancer immunotherapy often depends on recognition of peptide epitopes by cytotoxic T lymphocytes (CTLs). The tumor microenvironment (TME) is enriched for peroxynitrite (PNT), a potent oxidant produced by infiltrating myeloid cells and some tumor cells. We demonstrate that PNT alters the profile of MHC class I bound peptides presented on tumor cells. Only CTLs specific for PNT-resistant peptides have a strong antitumor effect in vivo, whereas CTLs specific for PNT-sensitive peptides are not effective. Therapeutic targeting of PNT in mice reduces resistance of tumor cells to CTLs. Melanoma patients with low PNT activity in their tumors demonstrate a better clinical response to immunotherapy than patients with high PNT activity. Our data suggest that intratumoral PNT activity should be considered for the design of neoantigen-based therapy and also may be an important immunotherapeutic target.

Phase I study of the histone deacetylase inhibitor entinostat in combination with 13-cis retinoic acid in patients with solid tumours

BACKGROUND

Preclinical studies suggest that histone deacetylase (HDAC) inhibitors may restore tumour sensitivity to retinoids. The objective of this study was to determine the safety, tolerability, and the pharmacokinetic (PK)/pharmacodynamic (PD) profiles of the HDAC inhibitor entinostat in combination with 13-cis retinoic acid (CRA) in patients with solid tumours.

METHODS

Patients with advanced solid tumours were treated with entinostat orally once weekly and with CRA orally twice daily × 3 weeks every 4 weeks. The starting dose for entinostat was 4 mg m(-2) with a fixed dose of CRA at 1 mg kg(-1) per day. Entinostat dose was escalated by 1 mg m(-2) increments. Pharmacokinetic concentrations of entinostat and CRA were determined by LC/MS/MS. Western blot analysis of peripheral blood mononuclear cells and tumour samples were performed to evaluate target inhibition.

RESULTS

A total of 19 patients were enroled. The maximum tolerated dose (MTD) was exceeded at the entinostat 5 mg m(-2) dose level (G3 hyponatremia, neutropenia, and anaemia). Fatigue (G1 or G2) was a common side effect. Entinostat exhibited substantial variability in clearance (147%) and exposure. CRA trough concentrations were consistent with prior reports. No objective responses were observed, however, prolonged stable disease occurred in patients with prostate, pancreatic, and kidney cancer. Data further showed increased tumour histone acetylation and decreased phosphorylated ERK protein expression.

CONCLUSION

The combination of entinostat with CRA was reasonably well tolerated. The recommended phase II doses are entinostat 4 mg m(-2) once weekly and CRA 1 mg kg(-1) per day. Although no tumour responses were seen, further evaluation of this combination is warranted.

Chemoprevention with enzastaurin: First-year results

1520

Background: Chemoprevention is crucial for reducing lung cancer mortality. The implementation and conduct of such trials is complex. We evaluated accrual in an ongoing trial. Methods: We are conducting a study evaluating if enzastaurin, a protein kinase C beta inhibitor, decreases the Ki-67 labeling index in bronchial epithelium after 6 months of therapy compared to placebo. Eligibility includes age 45 or younger, smoking 30 or fewer packs per year, quit for less than one 1 year, and bronchial meta/dysplasia. Results: Two-thousand eight hundred and nine potential subjects were selected from our database. Between December 2007 and November 2009, 1,242 were invited to participate by an introductory letter and at least 3 attempted telephone contacts. Phone contact was established with 621 (50%) subjects. 245 (39%) declined, 238 (38%) were ineligible, and 138 (22%) were interested in trial participation. At the first face-to-face visit, 57 out of 138 (38%) were eligible, 71 (51%) had not quit smoking for less than 1 year, one (1%) was ineligible for other reasons, and nine (7%) visits are pending. All 57 eligible subjects had an induced sputum exam: 36 had atypia, 19 were normal, and two were inadequate. Bronchoscopies with white light and laser-induced fluorescence and three or fewer biopsies have been done on 22 subjects (4 pending, 4 withdrew, 6 ineligible for bronch). Three had normal histology at all sites, 16 had metaplasia, and two had dysplasia in at least one site (84% abnormal bronchial histology rate, 1 pending). No occult cancers were identified. Conclusions: Of 1,242 preselected potential participants, 11% presented for a first face-to-face visit, 4.6% were eligible after a sputum exam, and 2.4% were fully eligible for randomization. Thus, to reach the accrual goal of 186 patients, we estimate that we will need to contact 7,700 subjects. During our 12-month period, we accessed 1,242 patients with 2.0 FTE for study coordinators (not including the pathologist, bronchoscopist, and laboratory personnel). Our expectation had been to accomplish accrual over a period of 42 months from a pool of 2,809 existing putative patients. Unless our eligibility rate of 2.4% increases, further sources of patients must be identified to accomplish our accrual goal.

No significant financial relationships to disclose.

Survival predictors after surgical resection of synchronous bilateral non-small cell lung cancers (NSCLC)

7517

Background: Non-small cell lung cancer (NSCLC) that presents with bilateral lung lesions, but without extra-thoracic metastasis, is uncommon. Prognosis is typically poor: No long-term survivor is expected with systemic chemotherapy. However, small reports have suggested the feasibility of bilateral resections. To date, the predictors of survival following this treatment approach remain unknown. Methods: Our institutional tumor registry was searched for patients who underwent bilateral resections of NSCLC during 1998–2006. Patients with metachronous presentations (second lesion found ≥ 2 years afterward) were excluded. Kaplan-Meier survival estimate and Cox proportional hazards model were used to identify survival predictors. Results: Of the 2582 patients operated for NSCLC, 50 patients were included in this analysis. Median age was 69.2 years. Median tumor sizes were 2.0 cms; Adenocarcinomas were the most common (51%). Of 103 thoracotomies, pneumonectomy was performed in 3 patients. Overall peri-operative mortality was 1.9%. Median progression-free survival was 46.0 months (95% CI, 33.1–66.6); overall survival was 77.5 months (95% CI, 43.1–111.1). Performance status, presence of comorbidity, and pathological vascular invasion were important prognostic factors (Table). Risk score based on the sum of these factors (present =1; absent =0) was a strong predictor of survival. Patients with score ≥ 2 (N=11) had a median survival of 17.2 months, compared with 83.5 months among those with score ≤ 1 (HR 5.52, 95% CI 2.27–13.46; p=0.0002). Conclusions: In this largest series of surgery for synchronous bilateral NSCLC to date, the overall survival rate at 5 years is approximately 50%. Performance status, comorbidity, and vascular invasion are strong predictors of survival. Patients with vascular invasion are at an increased risk of progression or death and adjuvant therapy should be considered.

[Table: see text]

No significant financial relationships to disclose.

Predicting and monitoring tumor response to epidermal growth factor receptor inhibitor gefitinib in patients with locally advanced esophageal adenocarcinoma

14112

Background: This study aimed to validate an ex vivo chemosensitivity assay to measure the pharmacodynamic effect of gefitinib on esophageal adenocarcinoma (EAC) prior to treatment with pre-operative concomitant chemoradiotherapy (CRT). Methods: A 14 day run-in period with 250 mg/day of gefitinib preceded CRT. Endoscopic biopsies (D 0 and 14) in 4 patients with T2–3N0/1M0/1a EAC were analyzed by ex vivo chemosensitivity assay. Day 0 tissue was exposed to gefitinib ex vivo, then tumor was exposed to gefitinib for 14 days in vivo (ie in the patient). Phosphorylation of the EGFR, raf/MEK/ERK and PI3/AKT pathways was measured by Western blot. Profiles were compared for correlation between ex vivo and in vivo exposure, and patterns were correlated with response to CRT. The effects were also characterized by immunohistochemistry (IHC). EGFR, K-Ras, and PI3K mutations, serum concentrations of gefitinib and PTEN status were measured as potential confounders. Results: One patient with stage T3N1 died of unexplained hemorrhage during surgery. Three had clinical and path stages of: T3N1/T0N0, T3N0/T3N0, T3N1/T2N1. Gefitinib levels were constant, confirming exposure of target tissue to the drug. Ex vivo exposure yielded four distinct pathway patterns. The exact same patterns were seen after in vivo exposure. No mutations were identified in exons 18–21 of the EGFR, exons 2/3 of K-ras or exons 9/22 of PI3K. PTEN levels were similar in all tumors. PCNA expression correlated with raf/MEK/ERK pathway inhibition, but not with inhibition of EGFR activity. IHC correlated with Western blot for expression of EGFR, and phospho- and total ERK levels. No correlation was observed between gefitinib effect and pathologic response to CRT. Conclusions: This study used a novel ex vivo chemosensitivity assay to demonstrate the activity of gefitinib to inhibit target in tumor tissue obtained from patients with EAC. The exact correlation of pre- and post-treatment profiles suggests potential use in the pre-treatment setting to predict in vivo effects of targeted therapies. This approach may facilitate the further refinement of patient selection to maximize potential benefit while sparing patients unlikely to respond to a given agent.

No significant financial relationships to disclose.

In vivo platform for translational drug development and biomarker discovery in pancreatic cancer

4000

While there are many new agents entering clinical development, there is very little data to prioritize which agents should be explored in pancreas cancer. Furthermore, often there is no information on biomarkers that may predict the activity of these drugs in pancreas cancer. In this project, we have generated a cohort of 30 pancreatic cancer xenografts by implanting in nude mice tumor materials from surgical specimens. Molecular studies show that a) these tumors maintain the genetic features of the originator cancer such as KRAS, p53 and DPC4 gene status; b) tumors represent the heterogeneity of pancreatic cancer well (there is not selection of any genotype in the xenograft ) and c) features do not changed over time. We have used this platform to explore the activity of a battery with a total of 10 new anticancer agents including inhibitors of MAPK, EGFR, mTOR, src kinase, Ras oncogene, mitosis regulators, angiogenesis, heat shock protein and hedgehog pathway inhibitors using a methodology similar to a two stage phase II clinical trial. All agents are tested against 10 xenografts. Those inactive are not explored anymore. Active agents are tested against the full set of tumors. Thus far we have shown that inhibitors of mTOR and MAPK have substantial activity in this model while Ras interacting agents and EGFR targeted drugs have no single agent activity. For active agents, we have characterized the tumors for potential strategies and biormarkers that may predict activity using both a target-focus approach as well as general profiling approach. Signaling inhibitors are more active in tumors with evidence of activation of the targeted pathway. In addition, ex vivo assays indicate that the ability to inhibit the targeted pathway is associated with agent activity. This information may help to prioritize agents for clinical development in pancreatic cancer.

[Table: see text]

Phase 1 pharmacokinetic and pharmacodynamic study of the histone deacetylase inhibitor MS-275 in combination with 13-cis retinoic acid in patients with advanced solid tumors

3055

Background: Preclinical studies suggest that histone deacetylase (HDAC) inhibitors may restore tumor sensitivity to retinoids. The objective of this study was to determine the maximum-tolerated dose (MTD), the dose-limiting toxicity (DLT), and the pharmacokinetic (PK)/pharmacodynamic (PD) profiles of the HDAC inhibitor MS-275 in combination with 13-cis retinoic acid (CRA). Methods: Patients (pts) with advanced solid tumors were treated with MS-275 orally once weekly and CRA orally twice daily x 3 weeks every 4 weeks. The starting dose for MS-275 was 4 mg/m2 and the dose was escalated based on toxicity assessments. The fixed dose for CRA was 1 mg/kg/day. PK concentrations of MS-275 and CRA were determined by LC/MS/MS. Western Blot analysis on peripheral-blood mononuclear cells (PBMCs) and tumor samples (when feasible) were performed to evaluate target inhibition. Results: To date thirteen pts have been enrolled. Tumor types include prostate (4 pts), bladder and renal cell (2 pts), and others. The MTD was exceeded at the 5 mg/m2 dose level (G3 hyponatremia, neutropenia and anemia). Fatigue (G1 or G2) is a common side effect. MS-275 peak concentrations were 141.6±75.7ng/mL at 4mg/m2 and 139.5±30.9 ng/mL at 5mg/m2. MS-275 half-life and clearance were 108.2±47.9h and 9.4±6.0L/h/m2, which is consistent with prior reports for MS-275 as single agent. Median CRA steady-state trough levels were 182.4 ng/mL. The MTD was 4 mg/m2 MS-275 and 1 mg/kg CRA. Five pts remained on treatment for ≥ 4 months including pts with prostate cancer (3), pancreatic cancer (6 months) and a pt with renal cell carcinoma (12 months) who presented a partial response in the lungs. Histones isolated from PBMCs showed transient but consistent protein acetylation post-therapy. Tumor biopsy of a liver lesion from prostate carcinoma revealed post-therapy induced histone acetylation and decreased phosphorylated ERK and STAT3 protein expression consistent with HDAC inhibitory activity. Conclusions: Combination of MS-275 with CRA is reasonably well tolerated and 4 mg/m2 is the Phase II recommended dose for MS-275 in combination with CRA. Tumor response and PD data suggest clinical and biological activity for this combination strategy.

[Table: see text]

Optimizing targeted agents development in pancreatic cancer: A fine-needle aspirate biopsy (FNAB) based ex vivo and in vivo assay

3002

Background: While targeted therapeutics effectively inhibit tumor growth with less toxicity than conventional chemotherapy, in general cancer patients show highly variable responses to them. This study aimed to develop and validate methods that permit the prediction and assessment of the efficacy of targeted therapeutics by using tumor fine needle aspiration biopsy (FNAB) samples Methods: A series of human primary pancreatic cancer were xenografted in nude mice by implanting tumor materials from surgically resected pancreatic cancer patients. Animals were treated with an epidermal growth factor receptor (EGFR) inhibitor, erlotinib, and the mTOR inhibitor temsirolimus or vehicle. Tumors were sampled by FNAB prior to (baseline) and after therapy. Tumor cells obtained by FNAB at baseline were exposed to erlotinib or temsirolimus for six hours ex vivo to prospectively predict tumor response. The degree of inhibition in phosphorylation of ERK1/2 and S6-Ribosomal Protein (S6-RP) downstream to EGFR and mTOR, respectively, were assessed by Western blot to determine the efficacy of the targeted drugs ex vivo and in vivo. The results were correlated with drug-mediated changes in tumor volumes. The effect of drugs on protein phosphorylation ex vivo was also analyzed in patient FNAB samples to show the clinical feasibility of the approach. Results: The degree of inhibition of target pathway activity in tumor cells treated with erlotinib or temsirolimus ex vivo closely correlates with tumor sensitivity in vivo. Xenograft animals sensitive to therapy showed the highest average inhibition of target protein phosphorylation in ex vivo assays, whereas tumors resistant to drugs gave the lowest one. Patient tumor samples yielded adequately cellular material to analyze the effect of erlotinib and temsirolimus in ex vivo assays. Conclusions: FNAB can be used to test ex vivo tumor response to targeted agents. These effects predicted pharmacodynamic as well as antitumor effects in a serie of pancreatic cancer xenografts. Implementation of these novel methods in clinical trials may be useful to identify patients that are likely to benefit from targeted therapeutics before being exposed to drugs and their potential side effects.

No significant financial relationships to disclose.

Heregulin induces phosphorylation of BRCA1 through phosphatidylinositol 3-Kinase/AKT in breast cancer cells

The breast cancer susceptibility gene BRCA1 encodes a nuclear phosphoprotein that acts as a tumor suppressor. Phosphorylation of BRCA1 has been implicated in altering its function, however, the pathway(s) that leads to the phosphorylation of BRCA1 has not been described. Here, a signaling pathway by which heregulin induces cell cycle-independent phosphorylation of BRCA1 was delineated. We showed that heregulin stimulation induced the phosphorylation of BRCA1 and concomitant activation of the serine/threonine kinase AKT in T47D human breast cancer cells. Heregulin-induced phosphorylation of BRCA1 was abrogated by phosphatidylinositol 3-kinase (PI3K) inhibitors and by a dominant-negative AKT. In the absence of heregulin, the ectopic expression of the constitutively active p110 subunit of PI3K was sufficient to induce BRCA1 phosphorylation. Furthermore, the purified glutathione S-transferase/AKT kinase phosphorylated BRCA1 in vitro. We have also shown that the phosphorylation of BRCA1 by AKT occurs on the residue Thr-509, which is located in the nuclear localization signal. These results reveal a novel signaling pathway that links extracellular signals to the phosphorylation of BRCA1 in breast cancer cells.

Regulation of gene expression in mammary epithelial cells by cellular confluence and sequence-specific DNA binding factors

Milk protein gene expression in mammary epithelial cells is regulated by interactions of the cells with each other and with extracellular-matrix components, and by the lactogenic hormones. Cell-cell and cell-extracellular-matrix interactions confer a state of competence to HC11 mammary epithelial cells. Cellular confluence and matrix deposition are prerequisites for the lactogenic hormone induction of, for example, beta-casein synthesis. We have studied how these cellular interactions influence transcription factor activity. Proximal and distal regulatory elements have been identified in the DNA of the beta-casein gene promoter that confer transcriptional induction to the lactogenic hormones in competent cells. A region located between positions -221 and -170 of the rat beta-casein promoter contains overlapping binding sites for DNA binding factors with positive and negative regulatory activity. A construct containing 221 nt of 5' promoter sequences linked to a chloramphenicol acetyltransferase (CAT) reporter gene and transfected into HC11 cells has low constitutive expression and is strongly inducible. Deletion of the sequences to -183 results in an increase in both constitutive and induced expression. Mutations in or deletion of the region from -183 to -170 abolish promoter activity. A sequence-specific single-stranded DNA binding transcriptional repressor (STR), composed of two proteins, binds to the upper strand of the -194 to -163 fragment and negatively regulates transcription. STR also recognizes the 5' untranslated region of the beta-casein mRNA and is sequestered into the cytoplasm by RNA after lactogenic hormone induction. Sequestration by RNA allows an activator to bind to the fragment -183 to -170. This activator has been identified as SARP, a sequence-specific single-stranded DNA activator region binding protein. The binding site of SARP is found both in the upper and the lower strands of this fragment. SARP has no affinity for RNA. It enhances transcription of a promoter construct containing rat beta-casein promoter sequences from -183 to -1 and of a heterologous promoter containing multimerized copies of the -194 to -163 fragment in a lactogenic-hormone-independent manner. Mutations between positions -183 and -170, which result in a loss of promoter activity, also prevent SARP from binding to the DNA. Confluence of HC11 cells up-regulates the DNA binding activity of SARP. High SARP activity is also detected in mammary gland cells of lactating mice and is regulated by suckling. Withdrawal of pups from their lactating mothers results in a rapid decrease of SARP activity. We have purified SARP from the lactating mammary tissue of sheep and have identified proteins of 28 and 35 kDa.

PPARgamma induces cell cycle withdrawal: inhibition of E2F/DP DNA-binding activity via down-regulation of PP2A

PPAR gamma is an adipose-selective nuclear hormone receptor that plays a key role in the control of adipocyte differentiation. Previous studies indicated that activation of ectopically expressed PPAR gamma induces differentiation when cells have ceased growth because of confluence. We show here that ligand activation of PPAR gamma is sufficient to induce growth arrest in fibroblasts and SV40 large T-antigen transformed, adipogenic HIB1B cells. Cell cycle withdrawal is accompanied by a decrease in the DNA-binding and transcriptional activity of the E2F/DP complex, which is attributable to an increase in the phosphorylation of these proteins, especially DP-1. This effect is a consequence of decreased expression of the catalytic subunit of the serine-threonine phosphatase PP2A. These data suggest an important role for PP2A in the control of E2F/DP activity and a new mode of cell cycle control in differentiation.

Heregulin-stimulated acetylcholine receptor gene expression in muscle: requirement for MAP kinase and evidence for a parallel inhibitory pathway independent of electrical activity

Binding of heregulin (HRG) to its receptor, ErbB3, results in a dimerization with ErbB2/neu and activation of their intrinsic tyrosine kinases, initiating a cascade of events resulting in the stimulation of acetylcholine receptor (AChR) genes in muscle. Here we have examined the signalling downstream of the HRG receptor. We show that phosphatidylinositol 3'-kinase (PI3K) and SHC bind to the HRG-activated ErbB3 in myotubes. Subsequently, p70S6 kinase (p70S6k), and MAP kinase ERK2 and thereby p90rsk are activated. However, inhibition of PI3K and p70S6k by wortmannin and rapamycin, respectively, failed to antagonize AChR alpha-subunit gene expression stimulated by HRG, despite the fact that the activities of the kinases were inhibited. In contrast, these inhibitors elevated AChR alpha-subunit mRNA levels, by themselves, independently of muscle electrical activity. On the other hand, the 17mer antisense oligonucleotide, EAS1, caused a specific depletion of ERK2 and eliminated the ability of HRG to stimulate AChR alpha-subunit gene expression. These results indicate that HRG stimulates expression of AChR genes via ERK2 activation, and provide a physiological example of neurotrophic factor-associated repression of AChR genes by stimulation of p70S6k activity which may contribute to the expression of adult type AChR genes at the neuromuscular junction.

Terminal differentiation of human liposarcoma cells induced by ligands for peroxisome proliferator-activated receptor gamma and the retinoid X receptor

Induction of terminal differentiation represents a promising therapeutic approach to certain human malignancies. The peroxisome proliferator-activated receptor gamma (PPAR gamma) and the retinoid X receptor alpha (RXR alpha) form a heterodimeric complex that functions as a central regulator of adipocyte differentiation. Natural and synthetic ligands for both receptors have been identified. We demonstrate here that PPAR gamma is expressed at high levels in each of the major histologic types of human liposarcoma. Moreover, primary human liposarcoma cells can be induced to undergo terminal differentiation by treatment with the PPAR gamma ligand pioglitazone, suggesting that the differentiation block in these cells can be overcome by maximal activation of the PPAR pathway. We further demonstrate that RXR-specific ligands are also potent adipogenic agents in cells expressing the PPAR gamma/RXR alpha heterodimer, and that simultaneous treatment of liposarcoma cells with both PPAR gamma- and RXR-specific ligands results in an additive stimulation of differentiation. Liposarcoma cell differentiation is characterized by accumulation of intracellular lipid, induction of adipocyte-specific genes, and withdrawal from the cell cycle. These results suggest that PPAR gamma ligands such as thiazolidinediones and RXR-specific retinoids may be useful therapeutic agents for the treatment of liposarcoma.

Adipocyte differentiation: a transcriptional regulatory cascade

The adipose cell is now known to play a complex role in energy homeostasis, energy storage and signaling to other tissues concerning the state of energy balance. The past few years have seen an explosive increase in our knowledge of the transcriptional basis of adipocyte differentiation. Factors such as peroxisome proliferator-activated receptor gamma, the CCAAT/enhancer binding protein family members, and adipocyte determination- and differentiation-dependent factor 1 play important regulatory roles in this process. Furthermore, these factors provide a focus for beginning to understand how various hormones and metabolites influence the development of adipose tissue in vivo.

beta-Casein mRNA sequesters a single-stranded nucleic acid-binding protein which negatively regulates the beta-casein gene promoter

beta-Casein gene expression in mammary epithelial cells is under the control of the lactogenic hormones, glucocorticoids, insulin, and prolactin. The hormonal control affects gene transcription, and several regulatory elements in the beta-casein gene promoter between positions -80 and -221 have previously been identified. A region located in the promoter between positions -170 and -221 contains overlapping sequences for negative and positive regulatory elements. A sequence-specific single-stranded DNA-binding factor (STR), composed of two proteins with molecular masses of 35 and 54 kDa, recognizes the upper strand of this region and has a repressing role in transcription. High-level STR binding activity was observed in nuclear extracts from mammary glands of pregnant and postlactating mice and from noninduced HC11 mammary epithelial cells, cells with a low level of transcriptional activity of the beta-casein gene. STR activity is downregulated in mammary epithelial cells during lactation of the animals and after lactogenic hormone induction of HC11 cells in culture. These cells strongly transcribe the beta-casein gene. We investigated the mechanism of downregulation and found that a lactogenic-hormone-induced molecule (I-STR) inhibits STR from binding to its DNA target. I-STR is composed of RNA. STR is sequestered into the cytoplasm by I-STR after lactogenic hormone induction of mammary epithelial cells and remains present in an RNA-bound form. A high-affinity STR binding site was found in the 5' untranslated region of beta-casein mRNA. We propose that beta-casein mRNA can function as I-STR. beta-Casein mRNA may positively regulate its own transcription by translocating STR from the nucleus to the cytoplasm. The beta-casein STR binding sequence increases expression of a transfected beta-galactosidase gene when it is placed into the 5' untranslated region sequence of the mRNA. STR may have a positive role in posttranscriptional regulation.

Hormonal regulation of transcription factor activity in mammary epithelial cells

The multihormonal control of milk protein gene transcription in mammary epithelial cells has been investigated. Although the hormones regulating milk protein gene expression are known, the interaction of the signal transduction pathways of steroid (glucocorticoids) and peptide (insulin and prolactin) hormones remains undefined in molecular terms. These signals converge on the level of nuclear factors binding to regulatory elements in the beta-casein gene promoter. The promoter has a modular architecture and is composed of positive and negative response elements. Nuclear transcription factors which bind to these elements have been identified. The mammary gland factor, MGF, is an essential mediator of lactogenic hormone action and is itself positively regulated in its DNA binding activity. It binds to the promoter region between positions -80 to -100. MGF counteracts a repressor element, constituted by two components, which is located adjacent to the MGF binding site at positions -100 to -150. The transcription factor YY1 binds to the proximal half of the repressor element which overlaps with the MGF binding site. Specific single-stranded DNA binding proteins contribute to the negative regulation of the promoter by interacting with sequence elements between -160 and -190. DNA binding of these proteins is negatively regulated by the lactogenic hormones.

Interaction of two sequence-specific single-stranded DNA-binding proteins with an essential region of the beta-casein gene promoter is regulated by lactogenic hormones

Transcription of the beta-casein gene in mammary epithelial cells is regulated by the lactogenic hormones insulin, glucocorticoids, and prolactin. The DNA sequence elements in the promoter which confer the action of the hormones on the transcriptional machinery and the nuclear proteins binding to this region have been investigated. We found that 221 nucleotides of promoter sequence 5' of the RNA start site are sufficient to mediate the induction of a chloramphenicol acetyltransferase reporter gene in transfected HC11 mammary epithelial cells. Deletion of 5' sequences to position -183 results in a construct with enhanced basal activity which still retains inducibility. A -170 beta-casein promoter-chloramphenicol acetyltransferase construct has very low transcriptional activity, which indicates the presence of a negative regulatory in the region between -221 and -183 and a positive regulatory element between -183 and -170. Band shift analysis showed that the promoter region between -194 and -163 specifically binds two nuclear proteins. The proteins are sequence-specific, single-stranded DNA-binding proteins which exclusively recognize the upper DNA strand and most likely play a repressing role in transcription. DNA binding activity of these nuclear proteins was observed only in nuclear extracts from mammary glands of mice in late pregnancy and postlactation, not during lactation. Hormonal control of the DNA binding activity of these proteins was also observed in the mammary epithelial cell line HC11. Mixing experiments showed that extracts from mammary tissue of lactating mice and from lactogenic hormone-treated HC11 cells contain an activity which can suppress the DNA binding of the single-stranded DNA-binding proteins.2+ identical specificity to the single-stranded DNA.

Effects of mitogenic agents upon glucocorticoid action in human tonsillar T-lymphocytes

The treatment of human tonsillar T-lymphocytes with 4-phorbol 12-myristate 13-acetate (PMA), resulted in about two fold increase in glucocorticoid receptor (GR) number, without any significant change in the receptor affinity. This increase disappeared in the presence of cycloheximide. Alone, PMA and calcium ionophore A23187 did not affect, but together stimulated, like phytohaemagglutinin (PHA), leucine and, in particular, thymidine incorporation. PMA enhanced slightly the stimulatory effect of PHA. Alone, these agents failed to alter the suppressive effect of dexamethasone on thymidine and leucine incorporation; however, PMA-A23187 and PMA-PHA combinations appeared to antagonize the suppression by dexamethasone.