The MUC1 HMFG1 glycoform is a precursor to the 214D4 glycoform in the human uterine epithelial cell line, HES

Expression of the transmembrane mucins, MUC1, MUC4 and MUC16, in normal endometrium and in endometriosis

STUDY QUESTION

Are the transmembrane mucins, MUC1, MUC4 and MUC16, differentially expressed in endometriosis compared with normal endometrium?

SUMMARY ANSWER

This study revealed that transmembrane mucin expression does not vary significantly in normal endometrium during the menstrual cycle and is not altered in endometriosis relative to the epithelial marker, cytokeratin-18 (KRT18).

WHAT IS KNOWN ALREADY

Increased serum levels of the transmembrane mucin fragments MUC1, MUC4 and MUC16 that normally dominate the apical surface of simple epithelia are found in several pathological conditions, including endometriosis. Altered mucin expression in gynecologic diseases may promote infertility or endometrial pathologies.

STUDY DESIGN, SIZE, DURATION

This was a laboratory-based study of samples from 12 endometriosis patients as well as non-endometriosis control samples obtained from 31 patients.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Total RNA was isolated from endometrial biopsies of ectopic and eutopic endometrium from women with endometriosis and control patients from different stages of the menstrual cycle. Quantitative (q)-RT-PCR analyses were performed for the mucins, MUC1, MUC4 and MUC16, relative to the epithelial marker, cytokeratin-18 (KRT18), or β-actin (ACTB). Frozen sections from endometrial biopsies of proliferative and mid-secretory stage women with endometriosis were immunostained for MUC1, MUC4 and MUC16.

MAIN RESULTS AND THE ROLE OF CHANCE

qRT-PCR analyses of MUC1 and MUC16 mRNA revealed that these mucins do not vary significantly during the menstrual cycle nor are they altered in women with endometriosis relative to the epithelial marker, KRT18. MUC4 mRNA is expressed at very low levels relative to MUC1 and MUC16 under all conditions. There was little difference in MUC1 and MUC16 expression between eutopic endometrial and ectopic endometriotic tissues. MUC4 expression also was not significantly higher in the ectopic endometriotic tissues. Immunostaining for all three mucins reveals robust expression of MUC1 and MUC16 at the apical surfaces of endometrial epithelia, but little to no staining for MUC4.

LIMITATIONS, REASONS FOR CAUTION

qRT-PCR analysis was the main method used for mucin detection. Additional studies with stage III-IV endometriotic tissue would be useful to determine if changes in MUC1 and MUC16 expression occur, or if MUC4 expression increases, at later stages of endometriosis.

WIDER IMPLICATIONS OF THE FINDINGS

We report a comprehensive comparative profile of the major transmembrane mucins, MUC1, MUC4 and MUC16, relative to the epithelial marker, KRT18, in normal cycling endometrium and in endometriosis, and indicate constitutive expression. Previous studies have profiled the expression of individual mucins relative to β-actin and indicate accumulation in the luteal phase. Thus, these differences in interpretation appear to reflect the increased epithelial content of endometrium during the luteal phase.

STUDY FUNDING

This study was supported by: NIH R01HD29963 to D.D.C.; NIH U54HD007495 to S.M.H.; and NIH R01HD067721 to S.L.Y. and B.A.L. The authors have no competing interests to declare.

The MUC1 extracellular domain subunit is found in nuclear speckles and associates with spliceosomes

MUC1 is a large transmembrane glycoprotein and oncogene expressed by epithelial cells and overexpressed and underglycosylated in cancer cells. The MUC1 cytoplasmic subunit (MUC1-C) can translocate to the nucleus and regulate gene expression. It is frequently assumed that the MUC1 extracellular subunit (MUC1-N) does not enter the nucleus. Based on an unexpected observation that MUC1 extracellular domain antibody produced an apparently nucleus-associated staining pattern in trophoblasts, we have tested the hypothesis that MUC1-N is expressed inside the nucleus. Three different antibodies were used to identify MUC1-N in normal epithelial cells and tissues as well as in several cancer cell lines. The results of immunofluorescence and confocal microscopy analyses as well as subcellular fractionation, Western blotting, and siRNA/shRNA studies, confirm that MUC1-N is found within nuclei of all cell types examined. More detailed examination of its intranuclear distribution using a proximity ligation assay, subcellular fractionation, and immunoprecipitation suggests that MUC1-N is located in nuclear speckles (interchromatin granule clusters) and closely associates with the spliceosome protein U2AF65. Nuclear localization of MUC1-N was abolished when cells were treated with RNase A and nuclear localization was altered when cells were incubated with the transcription inhibitor 5,6-dichloro-1-b-d-ribofuranosylbenzimidazole (DRB). While MUC1-N predominantly associated with speckles, MUC1-C was present in the nuclear matrix, nucleoli, and the nuclear periphery. In some nuclei, confocal microscopic analysis suggest that MUC1-C staining is located close to, but only partially overlaps, MUC1-N in speckles. However, only MUC1-N was found in isolated speckles by Western blotting. Also, MUC1-C and MUC1-N distributed differently during mitosis. These results suggest that MUC1-N translocates to the nucleus where it is expressed in nuclear speckles and that MUC1-N and MUC1-C have dissimilar intranuclear distribution patterns.

DNA profiling analysis of endometrial and ovarian cell lines reveals misidentification, redundancy and contamination

OBJECTIVES

Cell lines derived from human ovarian and endometrial cancers, and their immortalized non-malignant counterparts, are critical tools to investigate and characterize molecular mechanisms underlying gynecologic tumorigenesis, and facilitate development of novel therapeutics. To determine the extent of misidentification, contamination and redundancy, with evident consequences for the validity of research based upon these models, we undertook a systematic analysis and cataloging of endometrial and ovarian cell lines.

METHODS

Profiling of cell lines by analysis of DNA microsatellite short tandem repeats (STR), p53 nucleotide polymorphisms and microsatellite instability was performed.

RESULTS

Fifty-one ovarian cancer lines were profiled with ten found to be redundant and five (A2008, OV2008, C13, SK-OV-4 and SK-OV-6) identified as cervical cancer cells. Ten endometrial cell lines were analyzed, with RL-92, HEC-1A, HEC-1B, HEC-50, KLE, and AN3CA all exhibiting unique, uncontaminated STR profiles. Multiple variants of Ishikawa and ECC-1 endometrial cancer cell lines were genotyped and analyzed by sequencing of mutations in the p53 gene. The profile of ECC-1 cells did not match the EnCa-101 tumor, from which it was reportedly derived, and all ECC-1 isolates were genotyped as Ishikawa cells, MCF-7 breast cancer cells, or a combination thereof. Two normal, immortalized endometrial epithelial cell lines, HES cells and the hTERT-EEC line, were identified as HeLa cervical carcinoma and MCF-7 breast cancer cells, respectively.

CONCLUSIONS

Results demonstrate significant misidentification, duplication, and loss of integrity of endometrial and ovarian cancer cell lines. Authentication by STR DNA profiling is a simple and economical method to verify and validate studies undertaken with these models.

Cytokine and progesterone receptor interplay in the regulation of MUC1 gene expression

Mucin 1 (MUC1), a transmembrane mucin expressed at the apical surface of uterine epithelia, is a barrier to microbial infection and enzymatic attack. MUC1 loss at implantation sites appears to be required to permit embryo attachment and implantation in most species. MUC1 expression is regulated by progesterone (P) and proinflammatory cytokines, including TNFα and interferon γ (IFNγ). TNFα and IFNγ are highly expressed in uterine tissues under conditions where MUC1 expression is also high and activate MUC1 expression via their downstream transcription factors, nuclear factor (NF) κB and signal transducers and activators of transcription. P receptor (PR) regulates MUC1 gene expression in a PR isoform-specific fashion. Here we demonstrate that interactions among PR isoforms and cytokine-activated transcription factors cooperatively regulate MUC1 expression in a human uterine epithelial cell line, HES. Low doses of IFNγ and TNFα synergistically stimulate MUC1 promoter activity, enhance PRB stimulation of MUC1 promoter activity and cooperate with PRA to stimulate MUC1 promoter activity. Cooperative stimulation of MUC1 promoter activity requires the DNA-binding domain of the PR isoforms. MUC1 mRNA and protein expression is increased by cytokine and P treatment in HES cells stably expressing PRB. Using chromatin immunoprecipitation assays, we demonstrate efficient recruitment of NFκB, p300, SRC3 (steroid receptor coactivator 3), and PR to the MUC1 promoter. Collectively, our studies indicate a dynamic interplay among cytokine-activated transcription factors, PR isoforms and transcriptional coregulators in modulating MUC1 expression. This interplay may have important consequences in both normal and pathological contexts, e.g. implantation failure and recurrent miscarriages.

MUC1 is a substrate for gamma-secretase

Understanding the underlying mechanisms by which a normal cell avoids the oncogenic potential of MUC1 signaling requires further definition of the pathways by which the MUC1 cytoplasmic tail is processed in both normal and tumor-derived cells. In the present study we describe the processing pathway initiated by TACE/ADAM17 cleavage of MUC1. Utilizing the human uterine epithelial cell line, HES, derived from normal endometrium, we show that endogenous full length MUC1 undergoes regulated intramembranous proteolysis mediated by presenillin-dependent gamma-secretase. Cytokine-stimulated HES cells exposed to gamma-secretase inhibitors accumulated a membrane-associated 15 kDa fragment of the MUC1 C-terminal subunit (CTF15). Inhibitors of TACE/ADAM17-mediated shedding inhibited accumulation of MUC1-CTF15 and MUC1 ectodomain release to a similar extent consistent with MUC1-CTF15 being a product of TACE/ADAM17 action. Reduction of catalytically active gamma-secretase complex by nicastrin siRNA treatment also resulted in CTF15 accumulation. Furthermore, mature nicastrin, the substrate receptor for gamma-secretase, co-immunoprecipitated with CTF15 in the presence of gamma-secretase inhibitors indicating the formation of CTF15: nicastrin complexes. MUC1-CTF15 accumulation in response to gamma-secretase inhibition was demonstrated in both normal and tumor-derived cells from humans and mice indicating that this processing pathway exists in many cell contexts. We did not detect products of MUC1 cleavage by gamma-secretase in the presence of various proteasomal inhibitors indicating that subsequent degradation is either non-proteasomal or extremely efficient. We suggest that this efficient pathway attenuates potential signaling mediated by cytoplasmic tail fragments.

Novel forms of neurofascin 155 in the central nervous system: alterations in paranodal disruption models and multiple sclerosis

Stability of the myelin-axon unit is achieved, at least in part, by specialized paranodal junctions comprised of the neuronal heterocomplex of contactin and contactin-associated protein and the myelin protein neurofascin 155. In multiple sclerosis, normal distribution of these proteins is altered, resulting in the loss of the insulating myelin and consequently causing axonal dysfunction. Previously, this laboratory reported that mice lacking the myelin-enriched lipid sulphatide are characterized by a progressive deterioration of the paranodal structure. Here, it is shown that this deterioration is preceded by significant loss of neurofascin 155 clustering at the myelin paranode. Interestingly, prolonged electrophoretic separation revealed the existence of two neurofascin 155 bands, neurofascin 155 high and neurofascin 155 low, which are readily observed following N-linked deglycosylation. Neurofascin 155 high is observed at 7 days of age and reaches peak expression at one month of age, while neurofascin 155 low is first observed at 14 days of age and constantly increases until 5 months of age. Studies using conditional neurofascin knockout mice indicated that neurofascin 155 high and neurofascin 155 low are products of the neurofascin gene and are exclusively expressed by oligodendrocytes within the central nervous system. Neurofascin 155 high is a myelin paranodal protein while the distribution of neurofascin 155 low remains to be determined. While neurofascin 155 high levels are significantly reduced in the sulphatide null mice at 15 days, 30 days and 4 months of age, neurofascin 155 low levels remain unaltered. Although maintained at normal levels, neurofascin 155 low is incapable of preserving paranodal structure, thus indicating that neurofascin 155 high is required for paranodal stability. Additionally, comparisons between neurofascin 155 high and neurofascin 155 low in human samples revealed a significant alteration, specifically in multiple sclerosis plaques.

Expression of human MUC1 during early pregnancy in the human MUC1 transgenic mouse model

Embryo implantation involves direct interaction of the blastocyst with the luminal epithelium of the receptive uterus. MUC1, a transmembrane mucin expressed at the apical surface of uterine epithelia, acts as a barrier to microbial infection and enzymatic attack. Loss of MUC1 is believed to be a prerequisite for a functionally receptive uterus across many species. Human and murine MUC1 regulation by steroid hormones displays important differences. Estrogen (E2) stimulates MUC1 expression in mice, and progesterone (P4) antagonizes E2 action in this regard. MUC1 expression is severely reduced during the receptive uterine state in mice. In contrast, human MUC1 expression is maximal at the receptive or midluteal phase, when P4 levels are high. No information is available regarding regulation of human MUC1 in vivo at the site of embryo attachment. Our aim was to better understand regulation of human MUC1 during early pregnancy in vivo. For this purpose, we used a transgenic mouse carrying full-length human MUC1 gene (Tg(MUC1)79.24Gend) as well as endogenous MUC1 as a model system. Human MUC1 was detected by real-time RT-PCR, Western blotting, and immunohistochemistry during early pregnancy. Our data indicate that human MUC1 persists at reduced (20% relative to Day 1 postcoitum) levels in receptive-phase uteri, including the site of embryo attachment. In contrast, mouse MUC1 was much more severely (>98% relative to Day 1 postcoitum) reduced in the same context. These observations are consistent with distinct regulation between the human and mouse genes. Because these genes are expressed in the same transcriptional context (i.e., mouse uterine epithelia), structural differences between human and murine genes must account for these differences in MUC1 regulation.