Can Suica be used within Nagano?

I will be travelling to Tokyo, Karuizawa and Nagano. I will be using JR East Pass to travel between the 3 cities, as for exploring within the city itself, I understand that in Tokyo, Suica could be used for the local trains and buses. I am wondering if for travelling within Karuizawa and Nagano, can Suica be used for the cities' respective local transport. Also, can Suica be used in Nikko as well?

http://www.jreast.co.jp/e/pass/suica.html

I assume that it cannot be use in Nikko as it is not part of Tokyo Metropolitan area?
However I am not sure if Karuizawa and Nagano is part of Niigata area. I did some research online and there were people who said it can be used and others who said otherwise. Thus, I am unsure.

A place name is not enough, what transport company exactly?

Is Nagano means "Nagano City" and arond? if so,

Nagano :
It can not be used for Shinano Railway, Nagano electric railway and local buses.
Perhaps, it may have become available for use by some taxi companies,
but asking at tourist information office of stn is faster and gettiing free maps and more info easier.

Out of JR's stn houses in Karuizawa and Nagano city,
it can be used for shopping, restaurants, vending machines, coin lockers, etc.
However, it can not be used for public transportation.
(For local buses in Nagano city other IC card "KURURU" exist)
http://www.ic-kururu.jp/howto03.php

Seems payment for some hot spring(onsen) in hotel as day use etc but so many.
However, no way of searching even in Japanese.
https://www.jreast.co.jp/suicamoney/shopping/index.html
街ナカ(Machi-naka) means out of JR-East stns.
駅ナカ(Eki-naka) means inside of JR-East stn's ticket gate.
駅ビル(Eki-biru) means outside of JR-East stn's ticket gate of stn house or building.
(Click each big icons their company web will be opening as new window/tab.)

So, in 街ナカ of not urban big cities like mid Tokyo and around,
it would be better to think about "convenience stores(including recharge) is better".
Also you can be used for a major rental car, but in general use "credit card".

Nikko :
It can be used for Tobu railway(Not JR, except LtdExp fee)
and Tobu bus(tour and seasonal bus is excluded) as "PASMO" card service.
http://www.pasmo.co.jp/en/faq/#ancFAQPurchase01
Remember these stickers.
http://www.tobu-bus.com/pc/service/ic/images/stekker.gif
http://tabiris.com/wp1/images/2014/04/iccard-300x258.jpg

Taxi, Rental car, Shopping, restaurants and more are the same as 街ナカ.
Seems a bit comvenient than Nagano but also no complete list.
Although it can be used in some hotels and souvenir shops, but it is not all,
so recommend you to ask questions at tourist information office.

There are convenience stores anywhere, but it is not much more than like Tokyo.
Just say "conveni(=konbini コンビニ)" enough when asking to Japanese.
You can also search for the location at Google MAP like this.
https://goo.gl/maps/E2nxFcwKfUG2
In major JR stn houses in that area stands own conveni "NewDays" and "KIOSK" usual.
Out of JR stn, 7-Eleven, FamilyMart, LAWSON and some more are famous.
https://cdn-ak.f.st-hatena.com/images/fotolife/k/kiwipan/20170201/2017...
Newdays is in only JR-East stns mainly not so many numbers as nation wide market.
But in yr travel, you will see many times.

Recharge(only "Charge" enough in Japanese) at conveni and local bus, will be 1000Y steps.
https://youtu.be/TYwldhqBlS8 (Don't pick up until last success sound "Pi Pi'".)
(In local bus only accepted 1000Y note, no 2000,5000 and 10000Y, 500 also 100Y coins accepted)
JR-East(Suica provider) stns is 500Y steps, some PASMO rail companies 10Y steps.
https://i.ytimg.com/vi/xLuuE3Zn4DE/hqdefault.jpg

Note however that local Tobu trains around Nikko are covered by the JR East Pass (and also ltd exp trains to Shinjuku, but not those to Asakusa).