Schmidt et al. BMC Cancer 2014, 14:195 http://www.biomedcentral.com/1471-2407/14/195 RESEARCH ARTICLE Open Access Novel transcripts from a distinct promoter that encode the full-length AKT1 in human breast cancer cells Jeffrey W Schmidt1, Barbara L Wehde1, Kazuhito Sakamoto1, Aleata A Triplett1, William W West2 and Kay-Uwe Wagner1,2* Abstract Background: The serine-threonine kinase AKT1 plays essential roles during normal mammary gland development as well as the initiation and progression of breast cancer. AKT1 is generally considered a ubiquitously expressed gene, and its persistent activation is transcriptionally controlled by regulatory elements characteristic of housekeeping gene promoters. We recently identified a novel Akt1 transcript in mice (Akt1m), which is induced by growth factors and their signal transducers of transcription from a previously unknown promoter. The purpose of this study was to examine whether normal and neoplastic human breast epithelial cells express an orthologous AKT1m transcript and whether its expression is deregulated in cancer cells. Methods: Initial sequence analyses were performed using the UCSC Genome Browser and GenBank to assess the potential occurrence of an AKT1m transcript variant in human cells and to identify conserved promoter sequences that are orthologous to the murine Akt1m. Quantitative RT-PCR was used to determine the transcriptional activation of AKT1m in mouse mammary tumors as well as 41 normal and neoplastic human breast epithelial cell lines and selected primary breast cancers. Results: We identified four new AKT1 transcript variants in human breast cancer cells that are orthologous to the murine Akt1m and that encode the full-length kinase. These transcripts originate from an alternative promoter that is conserved between humans and mice. Akt1m is upregulated in the majority of luminal-type and basal-type mammary cancers in four different genetically engineered mouse models. Similarly, a subset of human breast cancer cell lines and primary breast cancers exhibited a higher expression of orthologous AKT1m transcripts. Conclusions: The existence of an alternative promoter that drives the expression of the unique AKT1m transcript may provide a mechanism by which the levels of AKT1 can be temporally and spatially regulated at particular physiological states, such as cancer, where a heightened activity of this kinase is required. Keywords: Human, Mice, Transgenic, Breast cancer, Mammary cancer, Proto-oncogene protein c-akt, Gene expression mRNA Background amplification or transcriptional upregulation (e.g., PIK3CA, The PI3-kinase/AKT pathway is one of the most fre- AKT1/3), transcriptional repression or deletion of negative quently altered signaling cascades in a large variety of regulators such as PTEN, as well as increased expression human cancers. The deregulated expression and activa- or activity of growth factors and their corresponding re- tion of signal transducers in this pathway can occur ceptors that signal through PI3K and AKT (e.g., IGF1, through various mechanisms such as hereditary or spor- HER2) [1]. This signaling cascade therefore has received adic mutations (e.g., PIK3CA, PIK3R1, AKT1/3, PDK1), considerable attention in drug targeting, but balancing efficacy with safety (i.e., the therapeutic index) has * Correspondence: [email protected] proved to be a considerable hurdle to overcome [2]. Ef- 1 Eppley Institute for Research in Cancer and Allied Diseases, University of forts directed at downregulating this pathway have fo- Nebraska Medical Center, 985950 Nebraska Medical Center, Omaha, NE 68198-5950, U.S.A cused largely on inhibiting protein function through 2Department of Pathology and Microbiology, University of Nebraska Medical small molecule inhibitors rather than on investigating Center, 985950 Nebraska Medical Center, Omaha, NE 68198-5950, U.S.A © 2014 Schmidt et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Schmidt et al. BMC Cancer 2014, 14:195 Page 2 of 12 http://www.biomedcentral.com/1471-2407/14/195 potential mechanisms for silencing PI3-kinase/AKT sig- State University). MMTV-neu transgenic mice [14] were naling through transcriptional downregulation. obtained from the Jackson Laboratory. Transgenic lines Similar to the PI3 kinase, AKT1 is generally considered that overexpress PRL in the mammary gland under the a ubiquitously expressed gene, and sequencing studies control of the neu-related lipocalin promoter [NRL-PRL] performed more than 20 years ago revealed that the were published previously [15]. Mammary tumors that AKT1 locus contains GC-rich regulatory elements char- arose spontaneously in aging females of these genetically acteristic of housekeeping gene promoters [3]. We re- engineered mouse strains were flash frozen and stored cently identified a novel Ak11 transcript (Akt1m) that is in liquid nitrogen. All animals used in this study were controlled by a previously unknown mammary-specific treated humanely and in accordance with institutional promoter in mice [4]. The new transcript includes a guidelines and federal regulations. This study was car- completely different 3′ untranslated exon and encodes ried out in strict accordance with the recommendations the full-length AKT1 protein with the ATG translation in the Guide for the Care and Use of Laboratory Ani- initiation codon in exon 2. Expression of Akt1m mRNA mals of the National Institutes of Health. The protocol from this promoter is controlled by prolactin and JAK2/ was approved by the Institutional Animal Care and Use STAT5 signaling and is upregulated more than 500-fold Committee of the University of Nebraska Medical during lactation compared to the virgin mammary gland, Center (IACUC#: 09-104-01, 03-104-01, and 12-008-03). contributing to more than a 7-fold increase in total Akt1 mRNA. The identification of this growth factor-induced Human breast cancer cell lines and tissue specimens promoter in mice provides a mechanism by which the A panel of 43 human breast cancer cell lines was ob- levels of AKT1 can be temporally and spatially regulated tained from the American Type Culture Collection at particular physiological states where heightened AKT1 (ATCC) with financial support from the Integrative Can- activity is required (e.g., during lactation when metabolic cer Biology Program at the National Cancer Institute needs are high). (NCI). Forty-one of these cell lines were expanded and It is an established fact that neoplastic cells hijack nor- maintained using media and supplements recommended mal developmental pathways to support their unique by ATCC. Deidentified flash-frozen human specimens metabolic requirements and to enhance cell prolifera- representing normal tissues of the breast, lung, liver, tion, survival, and migration [5]. Using human cell lines pancreas, and stomach as well as nine human breast and genetically engineered mice that are deficient in cancers representing the three major breast cancer sub- AKT1, it has been demonstrated that signaling through types (ERα-positive, ERBB2/HER2-positive, and triple- this serine-threonine kinase is critical for the initiation negative) were obtained under institutional guidelines and progression of breast cancer [6-8]. Since growth fac- from the tissue bank at the University of Nebraska Med- tors such as prolactin and their downstream effectors ical Center (UNMC). play key roles in mammary tumorigenesis [9,10], it is feasible to hypothesize that cancer cells aberrantly acti- mRNA expression analyses using quantitative vate the newly identified promoter to upregulate the real-time PCR transcriptional expression of Akt1. Given the histological Total RNA was extracted from flash-frozen tissues and and functional similarities of the mammary epithelium cell pellets using standard guanidinium thiocynate- as well as the requirement of identical molecular path- phenol-chloroform extraction or the RNeasy Mini Kit ways for the development of mammary glands in (Qiagen). The Super-Script II kit from Invitrogen with humans and mice, we postulated that the human gen- oligo-dT primers was used to perform the first-strand syn- ome might also contain an orthologous promoter that thesis according to the manufacture’s protocol. Quantita- contributes to the transcriptional regulation of the AKT1 tive real-time PCR (qPCR) was performed using iQ SYBR gene. If this is the case, these orthologous regulatory ele- green Supermix (Bio-Rad, Hercules, CA) and mRNA- ments might also be atypically activated in human breast specific forward primers for the mouse Akt1m (5′-GTC cancers. This line of investigation might provide insight GCC ACC TGC TTG CTG AGG-3′) and the human into the development of alternative strategies to modu- orthologous AKT1m (5′-CCT TCC TCG AGT CTG late the expression of AKT1 in neoplastic cells. GCC TG-3′). The reverse primers bind within the second coding exon of the mouse (5′-GGA CTC TCG CTG ATC Methods CAC ATC C-3′) and the human AKT1 (5′-GTA GCC Genetically modified mouse strains AAT GAA GGT GCC ATC-3′) cDNAs, respectively. The The generation and analysis of the MMTV-Cre-based qPCR reactions