First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping researchers promote themselves alongside their papers. Toan Le is first author on ‘ A ubiquitin–proteasome pathway degrades the inner nuclear membrane protein Bqt4 to maintain nuclear membrane homeostasis’, published in JCS. Toan is a PhD student in the lab of Yasushi Hiraoka at the Graduate School of Frontier Biosciences, Osaka University, Japan, investigating protein degradation at the inner nuclear membrane.

Toan Le

How would you explain the main findings of your paper in lay terms?

Within a eukaryotic cell, the nucleus, which houses the genome, is enclosed by a double-layered membrane known as the nuclear envelope. The inner layer of this membrane contains many proteins that play critical roles in the nucleus. In this study, we looked at one of these proteins, called Bqt4. Interestingly, we found that when there's too much Bqt4 at the inner nuclear membrane, the cell recognizes this as a problem. Thus, the cell eliminates the excess Bqt4 using a special protein degradation mechanism called the ubiquitin-proteasome system. Importantly, our findings revealed that this mechanism is vital for the cell because when Bqt4 is not being cleaned up properly and its level accumulates, it distorts the nuclear membrane and makes the cell less healthy. This suggests that having the right amount of Bqt4 protein is crucial for keeping the nuclear membrane in good shape.

Were there any specific challenges associated with this project? If so, how did you overcome them?

A primary challenge for me in this project was to determine whether the Cdc48 retrotranslocation complex played a role in the degradation of Bqt4. Initially, I attempted to introduce a mutation into Cdc48, which had previously been reported to be temperature sensitive in S. pombe, to observe its impact on Bqt4 degradation. To my surprise, however, this mutation had no detectable effect at the restrictive temperature of 36°C. I later learned that this particular Cdc48 mutation had been shown to be, in fact, a gain-of-function mutation, explaining why it did not hinder Bqt4 degradation as expected. Subsequently, I decided to find a different way to deal with the challenge. I introduced two mutations into both ATPase domains of Cdc48, as this had caused temperature-sensitivity in the budding yeast S. cerevisiae, in the hope that these mutations would similarly impair the ATPase of Cdc48 activity in S. pombe. Yet, to my surprise again, these mutations did not affect the level of Bqt4 at 36°C. Just when I almost wanted to give up, I noticed that the level of Bqt4 in this mutant appeared to be higher at lower temperatures. After double-checking, I realized that these mutations actually made the yeast cells become sensitive to cold, not heat. It turned out that the mutations significantly impeded Bqt4 degradation at the restrictive temperature of 16°C, indicating that Cdc48 was required for Bqt4 degradation.

When doing the research, did you have a particular result or ‘eureka’ moment that has stuck with you?

I noticed that when cells were treated with the proteasome inhibitor, the shape of the nuclear envelope became strikingly deformed. Although this phenomenon could have been a general consequence of proteasome inhibition, I had an intuitive feeling that it might be specifically caused by an elevated abundance of Bqt4, rather than any other proteins. Then it became a great moment for me when I observed that inhibition of the proteasomes in cells lacking Bqt4 did not result in the deformation of the nuclear envelope, in contrast to what occurred in wild-type cells. This finding strongly suggests that Bqt4 plays an essential role in the deformation of the nuclear envelope triggered by proteasomal inhibition. Consequently, this led me to hypothesize that Bqt4 indeed has a significant role in maintaining the morphology and homeostasis of the nuclear membrane.

Why did you choose Journal of Cell Science for your paper?

JCS has a great reputation for publishing high quality research in cell biology. I often read interesting papers in JCS on a regular basis. Furthermore, our lab has previously published two papers addressing the maintenance of nuclear membrane homeostasis in JCS. Therefore, I am delighted that my study, which explores another aspect of the same topic, has also found its place here.

Elevated levels of Bqt4 result in deformation of the nuclear envelope. Nuclear membranes are visualized with Ish1-GFP. The cells were treated with vehicle (+DMSO) or the proteasome inhibitor bortezomib (+BZ). Only when Bqt4 was present, was a strong deformation of the nuclear envelope observed upon proteasomal inhibition.

Elevated levels of Bqt4 result in deformation of the nuclear envelope. Nuclear membranes are visualized with Ish1-GFP. The cells were treated with vehicle (+DMSO) or the proteasome inhibitor bortezomib (+BZ). Only when Bqt4 was present, was a strong deformation of the nuclear envelope observed upon proteasomal inhibition.

Have you had any significant mentors who have helped you beyond supervision in the lab? How was their guidance special?

I had the privilege of pursuing my PhD in the lab of Professor Hiraoka, who granted me the freedom to conduct my research independently. In addition, Dr Hirano was a close mentor, who not only taught me the techniques when I first joined the lab, but also offered me invaluable assistance whenever I faced challenges, along with providing insightful guidance.

What motivated you to pursue a career in science, and what have been the most interesting moments on the path that led you to where you are now?

For me, there is nothing more meaningful, fascinating, and rewarding than making significant discoveries that contribute to our understanding of the natural world. One of the most captivating moments for me occurred during my junior high school years when I embarked on a self-guided exploration of chemistry. Armed with a university-level chemistry textbook, I attempted to do an electrolysis of saltwater experiment, using everyday items I could find around the house, such as a battery and copper wire. What happened then left an indelible impression on me as a young enthusiast, when instead of seeing the expected evolution of chlorine gas at the cathode, I observed the copper cathode dissolve and magically give rise to a yellow precipitate which I later identified as copper(I) hydroxide. This intriguing transformation fueled my passion and motivated me to pursue a career in science. As I continued my scientific journey, I ultimately decided to specialize in biology rather than chemistry, because how life occurs at the molecular level has always been what I am most curious and excited about.

Who are your role models in science? Why?

I admire scientists who are motivated solely by their curiosity to comprehend nature. In my early journey into the world of science, my initial role models were primarily physicists who fundamentally revolutionized our view of the microscopic world. Also, as a Vietnamese person, I was particularly inspired by Professor Dang Van Chi, who has made important discoveries in cancer biology.

What's next for you?

My aspiration is to embark on an academic career and establish myself as an independent scientist. Having obtained my PhD degree, I am in the process of searching for an ideal postdoctoral training opportunity that will enable me to conduct research that leads to meaningful and impactful discoveries.

Tell us something interesting about yourself that wouldn't be on your CV

It may appear unusual, but besides my profound interest in science, I am equally obsessed with history and linguistics. Additionally, I find great pleasure in music and literature.

Toan Le's contact details: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.

E-mail: lekhanhtoan88@gmail.com

Le
,
T. K.
,
Hirano
,
Y.
,
Asakawa
,
H.
,
Okamoto
,
K.
,
Fukagawa
,
T.
,
Haraguchi
,
T.
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Hiraoka
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Y.
(
2023
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A ubiquitin-proteasome pathway degrades the inner nuclear membrane protein Bqt4 to maintain nuclear membrane homeostasis
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J. Cell Sci.
136
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jcs260930
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