Khaled Machaca, Ph.D.

Professor of Physiology and Biophysics

  • Associate Dean for Research at WCM-Qatar

974 4492 8423

Location: WCM Qatar

Research Areas

Research Summary:

Welcome to Machaca Lab!

We are fascinated by the regulation of intracellular signaling pathways under both physiological and pathological conditions in the context of the regulation of oocyte maturation, meiotic arrest, cell cycle progression and secretion. We are particularly interested in Ca2+ signaling as a ubiquitous signaling module throughout phylogeny that is critical in mediating cellular responses to various cues. In fact, Ca2+signaling is often remodeled during cellular development and cellular pathology. Oocyte maturation in preparation for fertilization offers a classical example of remodeling of calcium signaling during development. Fully grown oocytes in the ovary are not fertilizable until they undergo oocyte maturation, which encompasses both entry into meiosis, and a cytoplasmic differentiation that includes a dramatic remodeling of the Ca2+signaling machinery. Ca2+ is the universal signal for egg activation at fertilization and for mediating the egg–to–embryo transition. Ca2+ signaling differentiation during oocyte maturation allows the egg to produce the specialized Ca2+ transient at fertilization to initiate egg activation. Ca2+ signaling remodeling affects both Ca2+ release and influx pathways including the IP3 receptor, the store-operated Ca2+ entry, the plasma membrane Ca2+ ATPase, and the Ca2+–activated Cl- channels (CaCC). We are interested in the complex interplay between these Ca2+ signaling modules and effectors in the context of meiosis progression. We are also investigating the regulation of Ca2+ signaling pathways at the cellular level in various pathological conditions and cell types, including vascular smooth muscle cells in hypertension; breast cancer metastasis; and the role of Ca2+ signaling in regulating metabolism.

Ca2+ signals often lead to different cellular responses in the same cell. This specificity is encoded in part in the spatial and temporal features of Ca2+ signals to activate subsets of downstream effectors leading to a defined cellular response. We are investigating the mechanisms controlling this specificity by focusing on the SOCE pathway and IP3-dependent Ca2+ release. We have recently described a novel Ca2+ signaling module that allows Ca2+ signaling in the mid-range spatially, between the classically defined Ca2+ micro-domain and global Ca2+ signals that cover the entire cell. Mid-range Ca2+ signaling occurs downstream of SOCE and uses ER tunnels to transport Ca2+ to specific effectors without inducing a global cytosolic Ca2+ rise (Ca2+ teleporting/tunneling). We have shown that CaCC are specifically activated by this pathway and are currently investigating other effectors.

Another emphasis in the Lab, consistent with the focus on signaling, is on the mechanisms controlling oocyte meiotic arrest in Xenopus. Vertebrate oocytes are arrested in prophase I for extended periods of time to allow for oocyte growth before maturation in preparation for fertilization. In Xenopus meiotic arrest is released in response to steroids particularly progesterone. We are interested in the mechanisms controlling meiotic arrest including the role of the progesterone receptor and the cAMP pathway and their interaction with the cell cycle kinase cascades.

Selected Publications:

  1. Carvacho I, Piesche M, Maier T, Machaca K. Ion channel function during oocyte maturation and fertilization. Frontiers in cell and developmental biology. 2018 Jun; 6(JUN):63. PMID: 29998105. PMCID: PMC6028574.
  2. El Najjar N, Kulkarni R, Nader N, Hodeify R, Machaca K. Effects of Hyperglycemia on Vascular Smooth Muscle Ca2+ Signaling. BioMed research international. 2017 Jun; 2017:3691349. PMID: 28713824. PMCID: PMC5497615.
  3. Petersen O, Courjaret R, Machaca K. Ca2+ tunnelling through the ER lumen as a mechanism for delivering Ca2+ entering via store-operated Ca2+ channels to specific target sites. The Journal of physiology. 2017 May; 595(10):2999. PMID: 28181236. PMCID: PMC5430212.
  4. Courjaret R, Dib M, Machaca K. Store-Operated Ca2+ Entry in Oocytes Modulate the Dynamics of IP3 -Dependent Ca2+ Release From Oscillatory to Tonic. Journal of cellular physiology. 2017 May; 232(5):1095. PMID: 27504787.
  5. Pasquier J, Gupta R, Rioult D, Hoarau-Véchot J, Courjaret R, Machaca K, Al Suwaidi J, Stanley E, Rafii S, Elliott D, Abi Khalil C, Tabrizi J. Coculturing with endothelial cells promotes in vitro maturation and electrical coupling of human embryonic stem cell-derived cardiomyocytes. The Journal of heart and lung transplantation : the official publication of the International Society for Heart Transplantation. 2017 Jan. PMID: 28169114.
  6. Rahal O, Fatfat M, Hankache C, Osman B, Khalife H, Machaca K, Muhtasib H. Chk1 and DNA-PK mediate TPEN-induced DNA damage in a ROS dependent manner in human colon cancer cells. Cancer biology & therapy. 2016 Oct; 1. PMID: 27690730. PMCID: PMC5137490.
  7. Nader N, Courjaret R, Dib M, Kulkarni R, Machaca K. Release from Xenopus oocyte prophase I meiotic arrest is independent of a decrease in cAMP levels or PKA activity. Development (Cambridge, England). 2016 Jun; 143(11):1926. PMID: 27122173.
  8. Ramadan S, Bendriss G, Hubrack S, Al-Abdulmalek A, Machaca K. A novel approach to the expression and purification of recombinant Xenopus Cdc25C. Protein expression and purification. 2016 Apr; 120:148. PMID: 26690375.
  9. Courjaret R, Hodeify R, Hubrack S, Ibrahim A, Dib M, Daas S, Machaca K. The Ca2+-activated Cl- channel Ano1 controls microvilli length and membrane surface area in the oocyte. Journal of cell science. 2016 Jan; 129(13):2548. PMID: 27173493.
  10. Aseervatham J, Tran L, Machaca K, Boudker O. The role of flexible loops in folding trafficking and activity of equilibrative nucleoside transporters. PloS one. 2015 Sep. PMID: 26406980. PMCID: PMC4583308.
  11. Hodeify R, Selvaraj S, Wen J, Arredouani A, Hubrack S, Dib M, Al-Thani S, McGraw T, Machaca K. A STIM1-dependent ‘trafficking trap’ mechanism regulates Orai1 plasma membrane residence and Ca²⁺ influx levels. Journal of cell science. 2015 Jan; 128(15):3143. PMID: 26116575.
  12. Fatfat M, Merhi R, Rahal O, Stoyanovsky D, Zaki A, Haidar H, Kagan V, Gali-Muhtasib H, Machaca K. Copper chelation selectively kills colon cancer cells through redox cycling and generation of reactive oxygen species. BMC cancer. 2014 Jul; 14(1):527. PMID: 25047035. PMCID: PMC4223620.
  13. Courjaret R, Machaca K. Mid-range Ca2+ signalling mediated by functional coupling between store-operated Ca2+ entry and IP3-dependent Ca2+ release. Nature communications. 2014 May; 5:3916. PMID: 24867608.
  14. Nader N, Dib M, Daalis A, Kulkarni R, Machaca K. Role for endocytosis of a constitutively active GPCR (GPR185) in releasing vertebrate oocyte meiotic arrest. Developmental biology. 2014 Jan; 395(2):355. PMID: 25220151.
  15. Ullah A, Jung P, Ullah G, Machaca K. The role of IP3 Receptor channel clustering in Ca2 + wave propagation during oocyte maturation. Progress in molecular biology and translational science. 2014 Jan; 123:83.
  16. Neri Q, Lee B, Rosenwaks Z, Machaca K, Palermo G. Understanding fertilization through intracytoplasmic sperm injection (ICSI). Cell calcium. 2014 Jan; 55(1):24. PMID: 24290744. PMCID: PMC4046257.
  17. Courjaret R, Hubrack S, Daalis A, Dib M, Machaca K. The Xenopus TRPV6 homolog encodes a Mg2+-permeant channel that is inhibited by interaction with TRPC1 Journal of cellular physiology. 2013 Dec; 228(12):2386. PMID: 23729281.
  18. Abou Saleh H, Pathan A, Daalis A, Hubrack S, Abou-Jassoum H, Al-Naeimi H, Rusch N, Machaca K. Inositol 145-trisphosphate (IP3) receptor up-regulation in hypertension is associated with sensitization of Ca2+ release and vascular smooth muscle contractility. The Journal of biological chemistry. 2013 Nov; 288(46):32941. PMID: 24097979. PMCID: PMC3829145.
  19. Yu F, Sun L, Hubrack S, Selvaraj S, Machaca K. Intramolecular shielding maintains the ER Ca2+ sensor stim1 in an inactive conformation. Journal of cell science. 2013 Jun; 126(11):2401. PMID: 23572507.
  20. Chaston D, Baillie B, Grayson T, Courjaret R, Heisler J, Lau K, Machaca K, Nicholson B, Ashton A, Matthaei K, Hill C. Polymorphism in endothelial connexin40 enhances sensitivity to intraluminal pressure and increases arterial stiffness. Arteriosclerosis, thrombosis, and vascular biology. 2013 May; 33(5):962. PMID: 23471232.