Biotin-dependent regulation of gene expression in human cells

Biotin conjugates in targeted drug delivery: is it mediated by a biotin transporter, a yet to be identified receptor, or (an)other unknown mechanism(s)?

Conjugation of drugs with biotin is a widely studied strategy for targeted drug delivery. The structure-activity relationship (SAR) studies through H3-biotin competition experiments conclude with the presence of a free carboxylic acid being essential for its uptake via the sodium-dependent multivitamin transporter (SMVT, the major biotin transporter). However, biotin conjugation with a payload requires modification of the carboxylic acid to an amide or ester group. Then, there is the question as to how/whether the uptake of biotin conjugates goes through the SMVT. If not, then what is the mechanism? Herein, we present known uptake mechanisms of biotin and its applications reported in the literature. We also critically analyse possible uptake mechanism(s) of biotin conjugates to address the disconnect between the results from SMVT-based SAR and "biotin-facilitated" targeted drug delivery. We believe understanding the uptake mechanism of biotin conjugates is critical for their future applications and further development.

Biotin attenuates heat shock factor 4b transcriptional activity by lysine 444 biotinylation

Genetic mutations in HSF4 cause congenital cataracts. HSF4 exhibits both positive and negative regulation on the transcription of heat shock and non-heat shock proteins during lens development, and its activity is regulated by posttranslational modifications. Biotin is an essential vitamin that regulates gene expression through protein biotinylation. In this paper, we report that HSF4b is negatively regulated by biotinylation. Administration of biotin or ectopic bacterial biotin ligase BirA increases HSF4b biotinylation at its C-terminal amino acids from 196 to 493. This attenuates the HSF4b-controlled expression of αB-crystallin in both lens epithelial cells and tested HEK293T cells. HSF4b interacts with holocarboxylase synthetase (HCS), a ubiquitous enzyme for catalyzing protein biotinylation in mammal. Ectopic HA-HCS expression downregulates HSF4b-controlled αB-crystallin expression. Lysine-mutation analyses indicate that HSF4b/K444 is a potential biotinylation site. Mutation K444R reduces the co-precipitation of HSF4b by streptavidin beads and biotin-induced reduction of αB-crystallin expression. Mutations of other lysine residues such as K207R/K209R, K225R, K288R, K294R and K355R in HSF4's C-terminal region do not affect HSF4's expression level and the interaction with streptavidin, but they exhibit distinct regulation on αB-crystallin expression through different mechanisms. HSF4/K294R leads to upregulation of αB-crystallin expression, while mutations K207R/K209R, K225R, K288R, K255R and K435R attenuate HSF4's regulation on αB-crystallin expression. K207R/K209R blocks HSF4 nuclear translocation, and K345R causes HSF4 destabilization. Taken together, the data reveal that biotin maybe a novel factor in modulating HSF4 activity through biotinylation.

•

Biotin downregulates HSF4's transcription activity.

•

HSF4 is associated with and down-regulated by holocarboxylase synthetase (HCS).

•

K444 is the potential biotinylated amino acid residue in HSF4b.

Convolutional neural network in proteomics and metabolomics for determination of comorbidity between cancer and schizophrenia

The association between cancer risk and schizophrenia is widely debated. Despite many epidemiological studies, there is still no strong evidence regarding the molecular basis for the comorbidity between these two pathological conditions. The vast majority of assays have been performed using clinical records of schizophrenic patients or those undergoing cancer treatment and monitored for sufficient time to find shared features between the considered conditions. We performed mass spectrometry-based proteomic and metabolomic investigations of patients with different cancer phenotypes (breast, ovarian, renal, and prostate) and patients with schizophrenia. The resulting vast quantity of proteomic and metabolomic data were then processed using systems biology and one-dimensional (1D) convolutional neural network (1DCNN) machine learning approaches. Traditional systematic approaches permit the segregation of schizophrenia and cancer phenotypes on the level of biological processes, while 1DCNN recognized "signatures" that could segregate distinct cancer phenotypes and schizophrenia at the comorbidity level. The designed network efficiently discriminated unrelated pathologies with a model accuracy of 0.90 and different subtypes of oncophenotypes with an accuracy of 0.94. The proposed strategy integrates systematic analysis of identified compounds and application of 1DCNN model for unidentified ones to reveal the similarity between distinct phenotypes.

Pyridoxine and pancreatic acinar cells: transport physiology and effect on gene expression profile

Pyridoxine (vitamin B₆), an essential micronutrient for normal cell physiology, plays an important role in the function of the exocrine pancreas. Pancreatic acinar cells (PACs) obtain vitamin B₆ from circulation, but little is known about the mechanism involved in the uptake process; limited information also exists on the effect of pyridoxine availability on the gene expression profile in these cells. We addressed both these issues in the current investigation using mouse-derived pancreatic acinar 266-6 cells (PAC 266-6) and human primary PACs (hPACs; obtained from organ donors), together with appropriate physiological and molecular (RNA-Seq) approaches. The results showed [³H]pyridoxine uptake to be 1) pH and temperature (but not Na⁺) dependent, 2) saturable as a function of concentration, 3) cis-inhibited by unlabeled pyridoxine and its close structural analogs, 4) trans-stimulated by unlabeled pyridoxine, 5) regulated by an intracellular Ca²⁺/calmodulin-mediated pathway, 6) adaptively-regulated by extracellular substrate (pyridoxine) availability, and 7) negatively impacted by exposure to cigarette smoke extract. Vitamin B₆ availability was found (by means of RNA-Seq) to significantly (FDR < 0.05) modulate the expression profile of many genes in PAC 266-6 cells (including those that are relevant to pancreatic health and development). These studies demonstrate, for the first time, the involvement of a regulatable and specific carrier-mediated mechanism for pyridoxine uptake by PACs; the results also show that pyridoxine availability exerts profound effects on the gene expression profile in mammalian PACs.

Targeting demyelination and virtual hypoxia with high-dose biotin as a treatment for progressive multiple sclerosis

Progressive multiple sclerosis (MS) is a severely disabling neurological condition, and an effective treatment is urgently needed. Recently, high-dose biotin has emerged as a promising therapy for affected individuals. Initial clinical data have shown that daily doses of biotin of up to 300 mg can improve objective measures of MS-related disability. In this article, we review the biology of biotin and explore the properties of this ubiquitous coenzyme that may explain the encouraging responses seen in patients with progressive MS. The gradual worsening of neurological disability in patients with progressive MS is caused by progressive axonal loss or damage. The triggers for axonal loss in MS likely include both inflammatory demyelination of the myelin sheath and primary neurodegeneration caused by a state of virtual hypoxia within the neuron. Accordingly, targeting both these pathological processes could be effective in the treatment of progressive MS. Biotin is an essential co-factor for five carboxylases involved in fatty acid synthesis and energy production. We hypothesize that high-dose biotin is exerting a therapeutic effect in patients with progressive MS through two different and complementary mechanisms: by promoting axonal remyelination by enhancing myelin production and by reducing axonal hypoxia through enhanced energy production. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Influences of dietary biotin and avidin on growth, survival, deficiency syndrome and hepatic gene expression of juvenile Nile tilapia Oreochromis niloticus

This study was undertaken to assess the interactive effects of dietary biotin and avidin on growth, feed conversion, survival and deficiency syndrome of tilapia and to determine the influence of dietary biotin deficiency on the expression of key genes related to biotin metabolism in tilapia. Six iso-nitrogenous and iso-energetic diets based on a common purified basal diet (vitamin-free casein as the protein source) were prepared for this study. The six dietary groups were 0 g avidin with 0 mg biotin (A0B0), 0 g avidin with 0.06 mg biotin/kg diet (A0B1), four avidin-supplemented diets incorporating at a incremental concentrations 0.25, 0.5, 1.0 and 2.0 g/kg diet with 0.06 mg biotin/kg diet (A15B1, A30B1, A60B1 and A120B1). Fish were hand-fed three times a day to apparent satiation for 12 weeks. Each diet was fed to three replicate groups of fish. Fish were kept in glass aquaria in a recirculating aquaculture system under standardized environmental conditions. Growth was significantly higher in fish that received the biotin-supplemented diet (A0B1), compared to diets lacking biotin or supplemented with avidin. Tilapia fed higher concentration of avidin-supplemented diets (A60B1 and A120B1) showed significant growth depression and displayed severe deficiency syndromes such as lethargy, anorexia, circular swimming and convulsions, which ultimately lead to death. There was a strong proportional linear relationship between the avidin content of the diet and feed conversion ratio, FCR (y = 0.43x + 0.135; r = 0.960; P < 0.001) and strong inverse relationship with protein efficiency ratio, PER (y = -0.309x + 2.195; r = 0.961; P < 0.0001). Elevated levels of biotinidase, pyruvate carboxylase, propionyl-CoA carboxylase-A and propionyl-CoA carboxylase-B transcripts were noted in fish fed all graded level of avidin-supplemented diets. A broken-line analysis indicated that feeding tilapia a diet with 44.5 times more avidin than the dietary biotin requirement can induce deficiency syndromes including retarded growth, when analyzing the data of percentage weight gain.

Effects of dietary biotin and avidin on growth, survival, feed conversion, biotin status and gene expression of zebrafish Danio rerio

A study was conducted to investigate the effects of dietary avidin on growth, survival, food conversion, biotin status and gene expression of zebrafish (Danio rerio Hamilton-Buchanan) juveniles (average wet mass 0.178 g) fed 7 purified diets for 12 weeks. Experimental diets were formulated to provide 0×, 1×, 15×, 30×, 60× and 120× excess avidin versus biotin kg(-1) diet, on a molar basis; a control diet contained neither supplemental biotin nor avidin. Fish fed the control diet had the lowest percentage weight gain and the highest mortality, while the highest percentage weight gain and the lowest mortality was observed with the 0× diet (P<0.05). A linear relationship was observed between feed conversion ratio (FCR) and dietary avidin (r=0.876; P<0.0001). Fish fed diets with 120× more avidin than biotin had the highest whole-body biotin content, while the lowest value was obtained with the control and avidin-free diets (P<0.05). Elevated levels of acetyl CoA carboxylase-A (acca), methylcrotonyl CoA carboxylase (mcc) and propionyl CoA carboxylase-A (pcca) transcripts were recorded in fish fed the control diet, in comparison to the other diets. A broken-line analysis indicated that feeding zebrafish a diet with 60 times more avidin than the dietary biotin requirement level will cause biotin deficiency signs.

Secretome-based identification and characterization of potential biomarkers in thyroid cancer

In search of thyroid cancer biomarkers, proteins secreted by thyroid cancer cell lines, papillary-derived TPC-1 and anaplastic-derived CAL62, were analyzed using liquid chromatography-tandem mass spectrometry. Of 46 high-confidence identifications, 6 proteins were considered for verification in thyroid cancer patients' tissue and blood. The localization of two proteins, nucleolin and prothymosin-α (PTMA), was confirmed in TPC-1 and CAL62 cells by confocal microscopy and immunohistochemically in xenografts of TPC-1 cells in NOD/SCID/γ mice and human thyroid cancers (48 tissues). Increased nuclear and cytoplasmic expression of PTMA was observed in anaplastic compared to papillary and poorly differentiated carcinomas. Nuclear expression of nucleolin was observed in all subtypes of thyroid carcinomas, along with faint cytoplasmic expression in anaplastic cancers. Importantly, PTMA, nucleolin, clusterin, cysteine-rich angiogenic inducer 61, enolase 1, and biotinidase were detected in thyroid cancer patients' sera, warranting future analysis to confirm their potential as blood-based thyroid cancer markers. In conclusion, we demonstrated the potential of secretome analysis of thyroid cancer cell lines to identify novel proteins that can be independently verified in cell lines, xenografts, tumor tissues, and blood samples of thyroid cancer patients. These observations support their potential utility as minimally invasive biomarkers for thyroid carcinomas and their application in management of these diseases upon future validation.

Holocarboxylase synthetase: correlation of protein localisation with biological function

Holocarboxylase synthetase (HCS) governs the cellular fate of the essential micronutrient biotin (Vitamin H or B7). HCS is responsible for attaching biotin onto the biotin-dependent enzymes that reside in the cytoplasm and mitochondria. Evidence for an alternative role, viz the regulation of gene expression, has also been reported. Recent immunohistochemical studies reported HCS is primarily nuclear, inconsistent with the location of HCS activity. Improved understanding of biotin biology demands greater knowledge about HCS. Here, we investigated the localisation of HCS and its isoforms. Three variants were observed that differ at the N-terminus. All HCS isoforms were predominantly non-nuclear, consistent with the distribution of biotin protein ligase activity. Unlike the longer constructs, the Met(58) isoform was also detected in the nucleus--a novel observation suggesting shuttling activity between nucleus and cytoplasm. We resolved that the previous controversies in the literature are due to specificity and detection limitations that arise when using partially purified antibodies.

Biotin is not a natural histone modification

In addition to its role as the cofactor of biotin-dependent carboxylases, biotin has been demonstrated to have a role in cellular processes including transcription and gene silencing. Histones have been proposed to be modified by biotin in a site-specific manner, providing a pathway by which biotin acts as a regulatory molecule for gene expression. However, there is uncertainty whether biotin attachment to histones in vitro can be extrapolated to biotin as a native histone modification. We critically examined a number of methods used to detect biotin attachment on histones, including [(3)H]-biotin uptake, Western blot analysis of histones, and mass spectrometry of affinity purified histone fragments with the objective of determining if the in vivo occurrence of histone biotinylation could be conclusively established. We found for each of these methods that, while biotin could be readily detected on native carboxylases or histones biotinylated in vitro, biotin attachment on native histones could not be detected in cell cultures from various sources. We conclude that biotin is absent in native histones to a sensitivity of at least one part per 100,000, suggesting that the regulatory impact of biotin on gene expression must be through alternate mechanisms.

Endogenous avidin biotin activity (EABA) in thyroid pathology: immunohistochemical study

Background

Immunohistochemical methods based on the high affinity of avidin and biotin (e.g. ABC, LSAB) are characterized by high sensitivity and are widely used for detection of immunologic reaction. However, a non-specific reaction, observed in frozen tissues and in paraffin-embedded material, increasing after heat induced epitope retrieval (HIER), and caused either by endogenous biotin or any another chemical compound with high affinity for avidin, may lead to diagnostic mistakes. The aim of our investigation is to study presence of endogenous avidin biotin activity (EABA) in thyrocytes originating from various thyroid pathological lesions (neoplastic and non-neoplastic).

Materials and methods

The immunohistochemical study was performed on paraffin-embedded specimens of surgically resected thyroid tissue from 97 patients with thyroid diseases: 65 patients with papillary carcinoma (PTC), 11 patients with nodular goiter in whom features of benign papillary hyperplasia were found, 9 with lymphocytic thyroiditis (LT), 8 with follicular adenoma, and 4 patients with follicular carcinoma. In PTC immunohistochemical study was performed both in primary tumors and in lymph node metastases. After HIER, incubation with streptavidin from LSAB+ (DakoCytomation) kit was done.

Results

Strong cytoplasmic EABA was observed in 56 of 65 (87.5%) PTC and in oxyphilic cells in 8 of 9 cases of LT. Significant correlation between EABA in primary PTC tumor and EABA in lymph node metastases was stated. Normal surrounding thyroid tissues showed absence or weak EABA. Aberrant intranuclear localization of biotin was noted in morules of cribriform-morular variant of PTC. No statistically significant correlation between patient's age, sex, metastases presence and EABA was observed.

Conclusion

Among thyroid lesions, false positive reactions are highly probable in papillary thyroid carcinoma and in lymphocytic thyroiditis if immunohistochemical detection is used on systems containing (strept)avidin. The most probable reason is the high endogenous biotin content.

Nitric oxide signaling depends on biotin in Jurkat human lymphoma cells

Biotin affects gene expression through a diverse array of cell signaling pathways. Previous studies provided evidence that cGMP-dependent signaling also depends on biotin, but the mechanistic sequence of cGMP regulation by biotin is unknown. Here we tested the hypothesis that the effects of biotin in cGMP-dependent cell signaling are mediated by nitric oxide (NO). Human lymphoid (Jurkat) cells were cultured in media containing deficient (0.025 nmol/L), physiological (0.25 nmol/L), and pharmacological (10 nmol/L) concentrations of biotin for 5 wk. Both levels of intracellular biotin and NO exhibited a dose-dependent relationship in regard to biotin concentrations in culture media. Effects of biotin on NO levels were disrupted by the NO synthase (NOS) inhibitor N-monomethyl-arginine. Biotin-dependent production of NO was linked with biotin-dependent expression of endothelial and neuronal NOS, but not inducible NOS. Previous studies revealed that NO is an activator of guanylate cyclase. Consistent with these previous observations, biotin-dependent generation of NO increased the abundance of cGMP in Jurkat cells. Finally, the biotin-dependent generation of cGMP increased protein kinase G activity. Collectively, the results of this study are consistent with the hypothesis that biotin-dependent cGMP signaling in human lymphoid cells is mediated by NO.

Cutaneous manifestations of nutritional deficiency

PURPOSE OF REVIEW

Nutritional deficiency, a global problem, remains uncommon in developed nations. Associated morbidity and mortality make it imperative that clinicians remain familiar with the clinical signs and symptoms of nutritional deficiencies to facilitate diagnosis. This article will review the cutaneous findings and recent literature regarding B12, niacin, zinc, vitamin A, kwashiorkor, biotin and selenium deficiencies, along with the clinical entities of noma and phrynoderma.

RECENT FINDINGS

Much of our understanding of the clinical manifestations of nutritional deficiencies comes from old literature; however, recent case reports and series have highlighted several patient populations that may be at risk from acquired deficiencies, including patients with anorexia nervosa, cystic fibrosis, patients receiving long-term tube-feeding and those with perceived or real food allergy. There can be significant clinical overlap between various micronutrient, protein and vitamin deficiencies. Additionally, providers should consider the possibility of multiple deficiencies coexisting in individual patients.

SUMMARY

Reports of nutritional deficiency continue to surface in developed nations and pediatricians need to have a basic understanding of their clinical manifestations. The skin is commonly affected and can be the presenting sign of illness. A higher clinical suspicion needs to be maintained in certain populations.