SETD2 is a protein known as a chromatin regenerator, one that helps turn genes on or off by altering histone proteins in the nucleus of the cell. When researchers found that SETD2 is reversed or lost in several types of cancer, usually a type of kidney cancer called clear-cell kidney cell carcinoma, all eyes turned to SETD2 activity in the cell cloud to explain these cancers.
In 2016, the laboratory of Dr. Cheryl Walker, director of the Center for Precision Environmental Health at Baylor College of Medicine, made the unexpected discovery that SETD2 not only regenerates chromosomes in the nucleus, but also microtubules of the cytoskeleton outside the nucleus. The cytoskeleton is a dynamic network of protein-fiber-like structures, consisting of filaments and microtubules that extend throughout the cell. It gives shape and organization within a cell and provides mechanical support that allows cells to perform essential functions such as division and movement.
The Walker team found that SETD2 tags cytoskeleton microtubules with a methyl group. Loss of SETD2 resulted in defective chromosome delivery and problems with daughter cell division during cell division.
“Our findings suggested that deficiencies in SETD2 may not only affect gene expression but also cytoskeleton-controlled functions, such as movement, metastasis and migration, which are very important for cancer cells,” Walker said. . “We were wondering if SETD2 could target other cytoskeletal proteins.”
SETD2 works with Huntingtin and actin to regulate cell migration
Actin proteins, which are filaments of the cytoskeleton, stood out as a primary target for SETD2. Two recent papers from Walker’s lab have now highlighted the role of SETD2 in altering the cytoskeleton actin and its impact on two important roles of cancer cells, cell migration and autophagy.
One of the first conclusions was that SETD2 interacts with the cytoskeleton actin and that it is able to alter actin in cells or in reactions using pure proteins. SETD2 attaches three methyl groups to actin at a location called lysine-68. Interestingly, they found that SETD2 interacted with two other proteins to methylate actin in cells: Huntingtin (HTT) and the actin binding adapter HIP1R.
Trimethylated lysine-68 regulates normal actin dynamics, including polymerization and depolymerization. Disturbance of the SETD2-HTT-HIP1R association inhibited actin methylation, causing defects in actin dinamics and unbalanced cell migration, an important function of cancer cells.
“These conclusions were very interesting because, to our knowledge, no one had studied the significance of the known SETD2-Huntingtin interaction for more than two decades,” said the first and co-author responsible Riyad Navroz Seervai, MD / Ph.D. a student in the Medical Specialist Training Program who completed his Ph.D. dissertation in Walker’s laboratory. “There was a limited list of papers about Huntingtin ‘s involvement in actin dinamics and cell migration, but enough to follow the SETD2-Huntingtin-actin link.”
Taken together, these data provided new insights into how defects in SETD2 and HTT can lead to disease by disrupting cytoskeletal methylation and deficiencies in cell migration. The researchers were also able to manipulate the SETD2-HTT-actin axis to show that changes in cell migration are specific to this new target of SETD2 (actin) rather than to chromatin or microtubules.
Read all about this work in the magazine Advances in science.
Role for SETD2 in autophagy
The group also studied the effect of SETD2 on autophagy, a device used by cells to remove unnecessary or abstract components.
“Dr. Walker’s lab has extensive experience and expertise in the study of autophagy,” Seervai said. “There was always a suspicion that SETD2 may be involved in this process, but it has not been confirmed. This project came to earth once we conducted the first tests looking for signs of autophagy and we found differences between cells with SETD2 function and those without. “
As they found when studying cell migration, concern about the ability of SETD2 to actin methylate at lysine-68 caused deficiencies in actin polymerization. In autophagy, actin polymerization altered the disruption of actin interactions with another protein called WHAMM. As a result, the cells had autophagy deficits. Importantly, no changes in gene expression were associated with autophagy, suggesting more room for SETD2 cytoskeleton mutation than its chromatin function.
Find all the details of this work in the magazine Biochemical and Biophysical Research Communication.
A fast-growing field of cell biology
“Actin modifications, such as the addition of methyl groups described here, have aptly been termed‘ Cinderella of the cytoskeleton ’and are no longer recognized as key regulators of cytoskeleton dynamics,” Seervai said. “But our findings and the results of other groups are changing this view. More researchers are showing interest in this new aspect of cytoskeleton regulation and we expect to find new findings identifying treatments. potential new conditions for conditions involving cytoskeleton deficiencies. “
Seervai was also involved in setting up a special interest subgroup at the ASCB / EMBO Cell Bio 2020 meaningful meeting on post-translational modifications of the cytoskeleton, including actin and tubulin. “Nearly 300 of us, including the president of ASCB, were at our session this year. From what I’ve heard, this is a sign that things have turned a corner for the field since a session like this took place. first set up several years ago. “
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Other contributors to this work include Menuka Karki, Rahul Jangid, Durga Nand Tripathi, In-Young Park, Sandra Grimm, Cristian Coarfa, and Sung Yun Jung from Baylor College of Medicine; Sarah Kearns, Kristen Verhey, and Michael Cianfrocco of the University of Michigan; Brian Millis and Matthew Tyska from Vanderbilt University; and Frank Mason and W. Kimryn Rathmell of Vanderbilt University Medical Center.
This work is supported by donations from the American Heart Association (19PRE34430069), the NIH (NCI-R35CA231993, R01CA203012, R35GM131744, P30ES023512, P30CA125123, NCI-CA125123, NIH-RR024574). RP170005, RP180672), Department of Defense (KC170259) and William and Ella Owens Medical Examination Foundation.