Thioesterase II, a new marker enzyme for human cells of breast epithelial origin

Human Milk Lipids and Small Metabolites: Maternal and Microbial Origins

Although there has been limited application in the field to date, human milk omics research continues to gain traction. Human milk lipidomics and metabolomics research is particularly important, given the significance of milk lipids and metabolites for infant health. For researchers conducting compositional milk analyses, it is important to consider the origins of these compounds. The current review aims to provide a summary of the existing evidence on the sources of human milk lipids and small metabolites. Here, we describe five major sources of milk lipids and metabolites: de novo synthesis from mammary cells, production by the milk microbiota, dietary consumption, release from non-mammary tissue, and production by the gut microbiota. We synthesize the literature to provide evidence and understanding of these pathways in the context of mammary gland biology. We recommend future research focus areas to elucidate milk lipid and small metabolite synthesis and transport pathways. Better understanding of the origins of human milk lipids and metabolites is important to improve translation of milk omics research, particularly regarding the modulation of these important milk components to improve infant health outcomes.

Hypoxia-induced transcriptional differences in African and Asian versus European diabetic cybrids

Diabetic retinopathy (DR) is the most common diabetic microvascular complication and cause of blindness in adults under the age of 65. Our results suggest that, when comparing transcriptomes of cultures grown in hypoxic conditions versus room-air, cybrids containing mitochondria from African and Asian diabetic subjects ([Afr + Asi]/DM) have some uniquely different transcriptome profiles compared to European/diabetic (Euro/DM) cybrids (e.g., fatty acid metabolism: EnrichR rank 10 in [Afr + Asi]/DM, rank 85 in Euro/DM; Endocytosis: rank 25 in [Afr + Asi]/DM, rank 5 in Euro/DM; Ubiquitin Mediated Proteolysis: rank 34 in [Afr + Asi]/DM, rank 7 in Euro/DM). As determined by both RNA-seq and qRT-PCR results, transcription of the gene encoding oleoyl-ACP hydrolase (OLAH) was significantly increased in [Afr + Asi]/DM cybrids compared to Euro/DM cybrids in hypoxic conditions. Additionally, our results show that in hypoxic conditions, Euro/DM cybrids and [Afr + Asi]/DM cybrids show similar decreases in ROS production. All cybrids showed decreased ZO1-minus protein levels, but their phagocytic functions were not significantly altered in hypoxic conditions. In conclusion, our findings suggest that the "molecular memory" imparted by [Afr + Asi]/DM mtDNA may act through one of the molecular pathways seen in transcriptome analysis, such as fatty acid metabolism, without significantly changing essential RPE functions.

Placental OLAH Levels Are Altered in Fetal Growth Restriction, Preeclampsia and Models of Placental Dysfunction

Previously, we identified elevated transcripts for the gene Oleoyl-ACP Hydrolase (OLAH) in the maternal circulation of pregnancies complicated by preterm fetal growth restriction. As placental dysfunction is central to the pathogenesis of both fetal growth restriction and preeclampsia, we aimed to investigate OLAH levels and function in the human placenta. We assessed OLAH mRNA expression (qPCR) throughout pregnancy, finding placental expression increased as gestation progressed. OLAH mRNA and protein levels (Western blot) were elevated in placental tissue from cases of preterm preeclampsia, while OLAH protein levels in placenta from growth-restricted pregnancies were comparatively reduced in the preeclamptic cohort. OLAH expression was also elevated in placental explant tissue, but not isolated primary cytotrophoblast cultured under hypoxic conditions (as models of placental dysfunction). Further, we discovered that silencing cytotrophoblast OLAH reduced the expression of pro- and anti-apoptosis genes, BAX and BCL2, placental growth gene, IGF2, and oxidative stress gene, NOX4. Collectively, these findings suggest OLAH could play a role in placental dysfunction and may be a therapeutic target for mitigating diseases associated with this vital organ. Further research is required to establish the role of OLAH in the placenta, and whether these changes may be a maternal adaptation or consequence of disease.

Crystal Structure and Substrate Specificity of Human Thioesterase 2: INSIGHTS INTO THE MOLECULAR BASIS FOR THE MODULATION OF FATTY ACID SYNTHASE

The type I fatty acid synthase (FASN) is responsible for the de novo synthesis of palmitate. Chain length selection and release is performed by the C-terminal thioesterase domain (TE1). FASN expression is up-regulated in cancer, and its activity levels are controlled by gene dosage and transcriptional and post-translational mechanisms. In addition, the chain length of fatty acids produced by FASN is controlled by a type II thioesterase called TE2 (E.C. 3.1.2.14). TE2 has been implicated in breast cancer and generates a broad lipid distribution within milk. The molecular basis for the ability of the TE2 to compete with TE1 for the acyl chain attached to the acyl carrier protein (ACP) domain of FASN is unknown. Herein, we show that human TE1 efficiently hydrolyzes acyl-CoA substrate mimetics. In contrast, TE2 prefers an engineered human acyl-ACP substrate and readily releases short chain fatty acids from full-length FASN during turnover. The 2.8 Å crystal structure of TE2 reveals a novel capping domain insert within the α/β hydrolase core. This domain is reminiscent of capping domains of type II thioesterases involved in polyketide synthesis. The structure also reveals that the capping domain had collapsed onto the active site containing the Ser-101-His-237-Asp-212 catalytic triad. This observation suggests that the capping domain opens to enable the ACP domain to dock and to place the acyl chain and 4'-phosphopantetheinyl-linker arm correctly for catalysis. Thus, the ability of TE2 to prematurely release fatty acids from FASN parallels the role of editing thioesterases involved in polyketide and non-ribosomal peptide synthase synthases.

Human mammary epithelial cells in culture: differentiation and transformation

Large quantities of normal and malignant human mammary epithelial tissues are readily available as surgical discard material. We have developed culture conditions that permit long term, active proliferation of these HMEC in a serum-free medium. Thus, large pools HMEC can be stored frozen for repetition of experiments from the same individual's cell population, and for use of the same cell pool by multiple investigators. Of all the specimens that we have thus far examined, we have observed no instances of spontaneous transformation to immortality, nor any karyotypic abnormalities in the cells derived from reduction mammoplasties. However, exposure of normal HMEC to the chemical carcinogen, benzo(a)pyrene did lead to expression of an extended life in culture, and two instances of transformation to immortality. These two established cell lines contain some chromosomal abnormalities, yet retain a relatively stable karyotype upon continued passage in culture. Transformation to malignancy was achieved by exposing these cell lines to tumor viruses and oncogenes. Both the normal HMEC, and the HMEC transformed in vitro, are now being utilized to understand the factors controlling expression of mammary specific properties, response to and production of various growth factors, and the nature of the progressive events leading to malignancy. The maximal usefulness of this, and other human epithelial cell systems, for elucidating the mechanisms of normal and diseased human cellular physiology will require continued efforts to optimize the culture conditions so that they resemble as closely as possible the processes occurring in humans in vivo.

Amino acid sequence of the serine active-site region of the medium-chain S-acyl fatty acid synthetase thioester hydrolase from rat mammary gland

Medium-chain S-acyl fatty acid synthetase thioester hydrolase (thioesterase II), a discrete monomeric enzyme of 29 kDa, regulates the product specificity of the de novo lipogenic systems in certain specialized mammalian and avian tissues, such as mammary and uropygial glands. The amino acid sequence of a 57-residue region containing the active site of the rat mammary gland enzyme has been established by a combination of amino acid and cDNA sequencing. Thioesterase II was radiolabeled with the serine esterase inhibitor [1,3-14C]diisopropyl-fluorophosphate and digested sequentially with cyanogen bromide, Staphylococcus aureus V8 protease and trypsin. A radiolabeled tryptic peptide was isolated and sequenced by automated Edman degradation and the location of the active-site residue established. The amino acid sequence was confirmed by sequencing an overlapping, unlabeled peptide, obtained by V8 digestion of the whole enzyme, and by dideoxynucleotide sequencing of a thioesterase II cDNA clone isolated from a lambda gt11 expression library. The active center contains the motif Gly-Xaa-Ser-Xaa-Gly, characteristic of the serine esterase family of enzymes. A seven-residue region around the essential serine of the rat mammary thioesterase II, Phe-Gly-Met-Ser-Phe-Gly-Ser, is completely homologous with a region of the mallard uropygial thioesterase, recently analyzed by cDNA sequencing, indicating that this is likely to be the active site of the avian enzyme. Overall homology between the mammalian and avian enzymes for the 57-amino-acid residue region is 47% and suggests that the two enzymes may share a common evolutionary origin.

Biological markers of breast cancer: a review

This review of biological markers of breast carcinoma has summarized a fairly representative series of studies pertaining to endocrine, carcinoembryonic, tissue-associated, serologic, biochemical, and specific tumor markers, with attention to some of the contributions from genetic engineering techniques applied to this research area. It is meant to be a helpful review with two purposes: those involved in research or clinical studies of breast cancer may wish to use this review as a basis for adding additional references in each category and to refer to the references provided for further study, thought, and synthesis of the data, perhaps to stimulate new associations between pertinent facts; those involved in the general scientific or clinical fields may wish to use it as an overview of biological markers pertaining to a particular form of cancer and perhaps this review will permit faster, more easily accessible synthesis of data, and a better understanding of a variety of parameters which are associated with breast cancer diseases.

Induction of transformation and continuous cell lines from normal human mammary epithelial cells after exposure to benzo[a]pyrene

Rapidly growing primary cultures of normal human mammary epithelial cells (HMEC) were exposed to 1 microgram of benzo[a]pyrene (B[a]P) per ml for two or three 24-hr periods. The B[a]P-treated populations consistently contained cells displaying a longer period of active growth in culture compared to the untreated control cells. Widespread heterogeneity in morphology and growth patterns was evidenced in these "extended life" (EL) cultures, with multiple sequential changes in these parameters occurring during the course of their life in culture. Two apparently immortal continuous cell lines have thus far emerged from these EL cultures. These lines have been characterized to be of human mammary epithelial origin and derived from the originally treated HMEC specimen. The continuous lines do not appear to be malignantly transformed as they do not cause tumor formation in nude mice and show little or no anchorage-independent growth. Nonetheless, they have acquired several properties characteristic of tumor-derived HMEC, which distinguish them from their normal progenitors. These cell lines, as well as the EL strains, may provide useful substrates for studies to determine what agents can induce further transforming events. Additionally, analysis of the multiple steps occurring in the El cultures, as well as in the emergence of the continuous cell lines, could potentially elucidate the processes occurring during human epithelial cell carcinogenesis and escape from senescence.